L1 and Ln cache: when are they written?Why can L3 caches hold only shared blocks?Multi-level cache for which inclusion holdsMESI Protocol Invalid cache line is attempted to be stored?Back invalidation to maintain inclusion in inclusive cacheComputer Architecture, cache hit and missesWhat if block sizes are not equal among caches?Pros and Cons of Average Memory Access Time When Increasing Cache Block SizeDirect-mapping cache questionCalculate Miss rate of L2 cache given global and L1 miss ratesSet Associative Cache Exercises
How can "mimic phobia" be cured or prevented?
Infinite dials to reset ever?
Is (0,1] a closed or open set?
What does "Scientists rise up against statistical significance" mean? (Comment in Nature)
Problem with TransformedDistribution
Why should universal income be universal?
A social experiment. What is the worst that can happen?
copy and scale one figure (wheel)
Count the occurrence of each unique word in the file
250 Floor Tower
How much character growth crosses the line into breaking the character
New brakes for 90s road bike
Aragorn's "guise" in the Orthanc Stone
Why can Carol Danvers change her suit colours in the first place?
Freedom of speech and where it applies
Rising and falling intonation
Why is it that I can sometimes guess the next note?
What is Cash Advance APR?
Why electric field inside a cavity of a non-conducting sphere not zero?
Dealing with a rejection from a journal
How should I respond when I lied about my education and the company finds out through background check?
What changes for testers when they are testing in agile environments?
What is going on with 'gets(stdin)' on the site coderbyte?
What should you do if you miss a job interview (deliberately)?
L1 and Ln cache: when are they written?
Why can L3 caches hold only shared blocks?Multi-level cache for which inclusion holdsMESI Protocol Invalid cache line is attempted to be stored?Back invalidation to maintain inclusion in inclusive cacheComputer Architecture, cache hit and missesWhat if block sizes are not equal among caches?Pros and Cons of Average Memory Access Time When Increasing Cache Block SizeDirect-mapping cache questionCalculate Miss rate of L2 cache given global and L1 miss ratesSet Associative Cache Exercises
$begingroup$
I have been following the "High Performance Computer Architecture" course from Georgia Tech (also on YouTube), and unless I've missed something, I cannot see where the following has been explained:
If I have a multilevel cache, L1/L2/L3/Ln:
1) what decides what level of this hierarchy a block fetched from memory initially gets put in?
2) If I evict a block from L1, does that mean it gets moved to L2 (replacing a block from L2 depending on the replacement policy), and so forth for L2 to L3, and L3 to Ln, until the block evicted from the last level cache gets written to memory?
PS And yes, I have searched for this, so don't downvote assuming I haven't :)
Update
After the answer given below, I went back to the video course and found this. It seems to suggest that data is initially fetched into the L2 cache, then "fed" to the L1 cache. This also shows how, without the inclusion bit set, L1 and L2 can become "out of sync".
3) Is this generally what happens in all caches? IE if I have a 7 layer cache, will the block be fetched into L7, then fed L7->L6, L6->L5 ... and finally L2->L1? This seems like a lot of work...
4) Except in the situation shown in the linked video (if the caches get "out of sync" then certain data will only be available in one cache even though it started out in both caches), it seems that having the same data in multiple levels of the cache all the time (i.e. when the inclusion bit is set) is a waste; we have to copy it amongst all the levels. This can't be the case though, so what am I missing?
cpu-cache
asked 4 hours ago
WadWad
1063
New contributor
Wad is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
add a comment |
$begingroup$
I have been following the "High Performance Computer Architecture" course from Georgia Tech (also on YouTube), and unless I've missed something, I cannot see where the following has been explained:
If I have a multilevel cache, L1/L2/L3/Ln:
1) what decides what level of this hierarchy a block fetched from memory initially gets put in?
2) If I evict a block from L1, does that mean it gets moved to L2 (replacing a block from L2 depending on the replacement policy), and so forth for L2 to L3, and L3 to Ln, until the block evicted from the last level cache gets written to memory?
PS And yes, I have searched for this, so don't downvote assuming I haven't :)
Update
After the answer given below, I went back to the video course and found this. It seems to suggest that data is initially fetched into the L2 cache, then "fed" to the L1 cache. This also shows how, without the inclusion bit set, L1 and L2 can become "out of sync".
3) Is this generally what happens in all caches? IE if I have a 7 layer cache, will the block be fetched into L7, then fed L7->L6, L6->L5 ... and finally L2->L1? This seems like a lot of work...
4) Except in the situation shown in the linked video (if the caches get "out of sync" then certain data will only be available in one cache even though it started out in both caches), it seems that having the same data in multiple levels of the cache all the time (i.e. when the inclusion bit is set) is a waste; we have to copy it amongst all the levels. This can't be the case though, so what am I missing?
cpu-cache
asked 4 hours ago
WadWad
1063
New contributor
Wad is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
add a comment |
$begingroup$
I have been following the "High Performance Computer Architecture" course from Georgia Tech (also on YouTube), and unless I've missed something, I cannot see where the following has been explained:
If I have a multilevel cache, L1/L2/L3/Ln:
1) what decides what level of this hierarchy a block fetched from memory initially gets put in?
2) If I evict a block from L1, does that mean it gets moved to L2 (replacing a block from L2 depending on the replacement policy), and so forth for L2 to L3, and L3 to Ln, until the block evicted from the last level cache gets written to memory?
PS And yes, I have searched for this, so don't downvote assuming I haven't :)
Update
After the answer given below, I went back to the video course and found this. It seems to suggest that data is initially fetched into the L2 cache, then "fed" to the L1 cache. This also shows how, without the inclusion bit set, L1 and L2 can become "out of sync".
3) Is this generally what happens in all caches? IE if I have a 7 layer cache, will the block be fetched into L7, then fed L7->L6, L6->L5 ... and finally L2->L1? This seems like a lot of work...
4) Except in the situation shown in the linked video (if the caches get "out of sync" then certain data will only be available in one cache even though it started out in both caches), it seems that having the same data in multiple levels of the cache all the time (i.e. when the inclusion bit is set) is a waste; we have to copy it amongst all the levels. This can't be the case though, so what am I missing?
cpu-cache
asked 4 hours ago
WadWad
1063
New contributor
Wad is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
I have been following the "High Performance Computer Architecture" course from Georgia Tech (also on YouTube), and unless I've missed something, I cannot see where the following has been explained:
If I have a multilevel cache, L1/L2/L3/Ln:
1) what decides what level of this hierarchy a block fetched from memory initially gets put in?
2) If I evict a block from L1, does that mean it gets moved to L2 (replacing a block from L2 depending on the replacement policy), and so forth for L2 to L3, and L3 to Ln, until the block evicted from the last level cache gets written to memory?
PS And yes, I have searched for this, so don't downvote assuming I haven't :)
Update
After the answer given below, I went back to the video course and found this. It seems to suggest that data is initially fetched into the L2 cache, then "fed" to the L1 cache. This also shows how, without the inclusion bit set, L1 and L2 can become "out of sync".
3) Is this generally what happens in all caches? IE if I have a 7 layer cache, will the block be fetched into L7, then fed L7->L6, L6->L5 ... and finally L2->L1? This seems like a lot of work...
4) Except in the situation shown in the linked video (if the caches get "out of sync" then certain data will only be available in one cache even though it started out in both caches), it seems that having the same data in multiple levels of the cache all the time (i.e. when the inclusion bit is set) is a waste; we have to copy it amongst all the levels. This can't be the case though, so what am I missing?
cpu-cache
cpu-cache
asked 4 hours ago
WadWad
1063
New contributor
Wad is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 4 hours ago
WadWad
1063
New contributor
Wad is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 44 mins ago
Wad
asked 4 hours ago
WadWad
1063
New contributor
Wad is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 4 hours ago
WadWad
1063
asked 4 hours ago
WadWad
1063
1063
New contributor
Wad is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
Wad is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Wad is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
$begingroup$
1) Usually any accessed data are saved into L1, independent whether they were previously available in L1, L2... or memory only.
For exclusive cache, data are stored ONLY in L1, for inclusive one, in the entire hierarchy. There are also mixed strategies. Also, some CPUs have "victim cache", which is extra cache level which gets ONLY data moved out of LLC (last level cache).
2) Yes, for write-back exclusive cache.
3) You misunderstood his explanation. He said that data are fetched and placed to both caches. Inclusion, btw, isn't the "bit set", but entire cache policy. The policy is built right into the hardware.
4) Exclusive cache better use precious space, but each time you have to bring new block into L1, you have to displace some block to L2, then some one to L3... and finally some one to memory. This means a lot of work. With inclusive cache, you just drop data from L1 cache, or replace older copy in L2 with newer copy displaced from L1.
As result, exclusive strategy is more optimal when adjacent cache levels has closer sizes (f.e. <=4x) and inclusive is better when sizes are very different.
answered 3 hours ago
BulatBulat
796410
$endgroup$
$begingroup$
Thanks for responding. I have updated the original question after reviewing your comment and using it to search the course I linked to: could you please check my update and update your answer? Thanks!
$endgroup$
– Wad
44 mins ago
$begingroup$
@Wad done......
$endgroup$
– Bulat
29 mins ago
$begingroup$
Thank you for taking the time to edit your answer. I don't understand 3) and 4) however, sorry. 3) So in an N level cache, what level is written to first when we have a miss? Is it N? And if so, is that same block copied to all higher levels? 4) Regarding exclusive, why do you need to displace from L1 to L2? Is this what I questioned in 2) above that you answered? Inclusion: surely this involves the most work, copying a block across all N caches??
$endgroup$
– Wad
10 mins ago
add a comment |
Your Answer
StackExchange.ifUsing("editor", function ()
return StackExchange.using("mathjaxEditing", function ()
StackExchange.MarkdownEditor.creationCallbacks.add(function (editor, postfix)
StackExchange.mathjaxEditing.prepareWmdForMathJax(editor, postfix, [["$", "$"], ["\\(","\\)"]]);
);
);
, "mathjax-editing");
StackExchange.ready(function()
var channelOptions =
tags: "".split(" "),
id: "419"
;
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function()
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled)
StackExchange.using("snippets", function()
createEditor();
);
else
createEditor();
);
function createEditor()
StackExchange.prepareEditor(
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: false,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: null,
bindNavPrevention: true,
postfix: "",
imageUploader:
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
,
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
);
);
Wad is a new contributor. Be nice, and check out our Code of Conduct.
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fcs.stackexchange.com%2fquestions%2f105949%2fl1-and-ln-cache-when-are-they-written%23new-answer', 'question_page');
);
Post as a guest
Required, but never shown
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
1) Usually any accessed data are saved into L1, independent whether they were previously available in L1, L2... or memory only.
For exclusive cache, data are stored ONLY in L1, for inclusive one, in the entire hierarchy. There are also mixed strategies. Also, some CPUs have "victim cache", which is extra cache level which gets ONLY data moved out of LLC (last level cache).
2) Yes, for write-back exclusive cache.
3) You misunderstood his explanation. He said that data are fetched and placed to both caches. Inclusion, btw, isn't the "bit set", but entire cache policy. The policy is built right into the hardware.
4) Exclusive cache better use precious space, but each time you have to bring new block into L1, you have to displace some block to L2, then some one to L3... and finally some one to memory. This means a lot of work. With inclusive cache, you just drop data from L1 cache, or replace older copy in L2 with newer copy displaced from L1.
As result, exclusive strategy is more optimal when adjacent cache levels has closer sizes (f.e. <=4x) and inclusive is better when sizes are very different.
answered 3 hours ago
BulatBulat
796410
$endgroup$
$begingroup$
Thanks for responding. I have updated the original question after reviewing your comment and using it to search the course I linked to: could you please check my update and update your answer? Thanks!
$endgroup$
– Wad
44 mins ago
$begingroup$
@Wad done......
$endgroup$
– Bulat
29 mins ago
$begingroup$
Thank you for taking the time to edit your answer. I don't understand 3) and 4) however, sorry. 3) So in an N level cache, what level is written to first when we have a miss? Is it N? And if so, is that same block copied to all higher levels? 4) Regarding exclusive, why do you need to displace from L1 to L2? Is this what I questioned in 2) above that you answered? Inclusion: surely this involves the most work, copying a block across all N caches??
$endgroup$
– Wad
10 mins ago
add a comment |
$begingroup$
1) Usually any accessed data are saved into L1, independent whether they were previously available in L1, L2... or memory only.
For exclusive cache, data are stored ONLY in L1, for inclusive one, in the entire hierarchy. There are also mixed strategies. Also, some CPUs have "victim cache", which is extra cache level which gets ONLY data moved out of LLC (last level cache).
2) Yes, for write-back exclusive cache.
3) You misunderstood his explanation. He said that data are fetched and placed to both caches. Inclusion, btw, isn't the "bit set", but entire cache policy. The policy is built right into the hardware.
4) Exclusive cache better use precious space, but each time you have to bring new block into L1, you have to displace some block to L2, then some one to L3... and finally some one to memory. This means a lot of work. With inclusive cache, you just drop data from L1 cache, or replace older copy in L2 with newer copy displaced from L1.
As result, exclusive strategy is more optimal when adjacent cache levels has closer sizes (f.e. <=4x) and inclusive is better when sizes are very different.
answered 3 hours ago
BulatBulat
796410
$endgroup$
$begingroup$
Thanks for responding. I have updated the original question after reviewing your comment and using it to search the course I linked to: could you please check my update and update your answer? Thanks!
$endgroup$
– Wad
44 mins ago
$begingroup$
@Wad done......
$endgroup$
– Bulat
29 mins ago
$begingroup$
Thank you for taking the time to edit your answer. I don't understand 3) and 4) however, sorry. 3) So in an N level cache, what level is written to first when we have a miss? Is it N? And if so, is that same block copied to all higher levels? 4) Regarding exclusive, why do you need to displace from L1 to L2? Is this what I questioned in 2) above that you answered? Inclusion: surely this involves the most work, copying a block across all N caches??
$endgroup$
– Wad
10 mins ago
add a comment |
$begingroup$
1) Usually any accessed data are saved into L1, independent whether they were previously available in L1, L2... or memory only.
For exclusive cache, data are stored ONLY in L1, for inclusive one, in the entire hierarchy. There are also mixed strategies. Also, some CPUs have "victim cache", which is extra cache level which gets ONLY data moved out of LLC (last level cache).
2) Yes, for write-back exclusive cache.
3) You misunderstood his explanation. He said that data are fetched and placed to both caches. Inclusion, btw, isn't the "bit set", but entire cache policy. The policy is built right into the hardware.
4) Exclusive cache better use precious space, but each time you have to bring new block into L1, you have to displace some block to L2, then some one to L3... and finally some one to memory. This means a lot of work. With inclusive cache, you just drop data from L1 cache, or replace older copy in L2 with newer copy displaced from L1.
As result, exclusive strategy is more optimal when adjacent cache levels has closer sizes (f.e. <=4x) and inclusive is better when sizes are very different.
answered 3 hours ago
BulatBulat
796410
$endgroup$
1) Usually any accessed data are saved into L1, independent whether they were previously available in L1, L2... or memory only.
For exclusive cache, data are stored ONLY in L1, for inclusive one, in the entire hierarchy. There are also mixed strategies. Also, some CPUs have "victim cache", which is extra cache level which gets ONLY data moved out of LLC (last level cache).
2) Yes, for write-back exclusive cache.
3) You misunderstood his explanation. He said that data are fetched and placed to both caches. Inclusion, btw, isn't the "bit set", but entire cache policy. The policy is built right into the hardware.
4) Exclusive cache better use precious space, but each time you have to bring new block into L1, you have to displace some block to L2, then some one to L3... and finally some one to memory. This means a lot of work. With inclusive cache, you just drop data from L1 cache, or replace older copy in L2 with newer copy displaced from L1.
As result, exclusive strategy is more optimal when adjacent cache levels has closer sizes (f.e. <=4x) and inclusive is better when sizes are very different.
answered 3 hours ago
BulatBulat
796410
edited 16 mins ago
answered 3 hours ago
BulatBulat
796410
answered 3 hours ago
BulatBulat
796410
answered 3 hours ago
BulatBulat
796410
796410
$begingroup$
Thanks for responding. I have updated the original question after reviewing your comment and using it to search the course I linked to: could you please check my update and update your answer? Thanks!
$endgroup$
– Wad
44 mins ago
$begingroup$
@Wad done......
$endgroup$
– Bulat
29 mins ago
$begingroup$
Thank you for taking the time to edit your answer. I don't understand 3) and 4) however, sorry. 3) So in an N level cache, what level is written to first when we have a miss? Is it N? And if so, is that same block copied to all higher levels? 4) Regarding exclusive, why do you need to displace from L1 to L2? Is this what I questioned in 2) above that you answered? Inclusion: surely this involves the most work, copying a block across all N caches??
$endgroup$
– Wad
10 mins ago
add a comment |
$begingroup$
Thanks for responding. I have updated the original question after reviewing your comment and using it to search the course I linked to: could you please check my update and update your answer? Thanks!
$endgroup$
– Wad
44 mins ago
$begingroup$
@Wad done......
$endgroup$
– Bulat
29 mins ago
$begingroup$
Thank you for taking the time to edit your answer. I don't understand 3) and 4) however, sorry. 3) So in an N level cache, what level is written to first when we have a miss? Is it N? And if so, is that same block copied to all higher levels? 4) Regarding exclusive, why do you need to displace from L1 to L2? Is this what I questioned in 2) above that you answered? Inclusion: surely this involves the most work, copying a block across all N caches??
$endgroup$
– Wad
10 mins ago
$begingroup$
Thanks for responding. I have updated the original question after reviewing your comment and using it to search the course I linked to: could you please check my update and update your answer? Thanks!
$endgroup$
– Wad
44 mins ago
$begingroup$
Thanks for responding. I have updated the original question after reviewing your comment and using it to search the course I linked to: could you please check my update and update your answer? Thanks!
$endgroup$
– Wad
44 mins ago
$begingroup$
@Wad done......
$endgroup$
– Bulat
29 mins ago
$begingroup$
@Wad done......
$endgroup$
– Bulat
29 mins ago
$begingroup$
Thank you for taking the time to edit your answer. I don't understand 3) and 4) however, sorry. 3) So in an N level cache, what level is written to first when we have a miss? Is it N? And if so, is that same block copied to all higher levels? 4) Regarding exclusive, why do you need to displace from L1 to L2? Is this what I questioned in 2) above that you answered? Inclusion: surely this involves the most work, copying a block across all N caches??
$endgroup$
– Wad
10 mins ago
$begingroup$
Thank you for taking the time to edit your answer. I don't understand 3) and 4) however, sorry. 3) So in an N level cache, what level is written to first when we have a miss? Is it N? And if so, is that same block copied to all higher levels? 4) Regarding exclusive, why do you need to displace from L1 to L2? Is this what I questioned in 2) above that you answered? Inclusion: surely this involves the most work, copying a block across all N caches??
$endgroup$
– Wad
10 mins ago
add a comment |
Wad is a new contributor. Be nice, and check out our Code of Conduct.
Wad is a new contributor. Be nice, and check out our Code of Conduct.
Wad is a new contributor. Be nice, and check out our Code of Conduct.
Wad is a new contributor. Be nice, and check out our Code of Conduct.
Thanks for contributing an answer to Computer Science Stack Exchange!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
Use MathJax to format equations. MathJax reference.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fcs.stackexchange.com%2fquestions%2f105949%2fl1-and-ln-cache-when-are-they-written%23new-answer', 'question_page');
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
