A procedure of caching data in linux kernel, especially on LLC
I wonder how kernel puts data on LLC or L3 caches in detail. I have been searching the information about using cache in kernel but many results talk about page cache or buffered cache but in this question it is only related to cache above the main memory.
Assume that I make a working set or data structure (30MB) in the kernel context by using kmalloc, vmalloc or whatever. What I am thinking is that there might be a different procedure such as protection or extra optimization to prevent any memory violation in kernel unlike using malloc or mmap in user context.
Therefore, if I make a same-size working set(30MB) using user library(malloc) in user mode, I would expect that I might get different performance when I access this data in the working set.
Question
1. How kernel uses LLC cache?
2. Can I get different performance when I allocate memory using malloc?
Any comments or materials would be appreciated :)
linux kernel
asked 58 mins ago
vincentc
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I wonder how kernel puts data on LLC or L3 caches in detail. I have been searching the information about using cache in kernel but many results talk about page cache or buffered cache but in this question it is only related to cache above the main memory.
Assume that I make a working set or data structure (30MB) in the kernel context by using kmalloc, vmalloc or whatever. What I am thinking is that there might be a different procedure such as protection or extra optimization to prevent any memory violation in kernel unlike using malloc or mmap in user context.
Therefore, if I make a same-size working set(30MB) using user library(malloc) in user mode, I would expect that I might get different performance when I access this data in the working set.
Question
1. How kernel uses LLC cache?
2. Can I get different performance when I allocate memory using malloc?
Any comments or materials would be appreciated :)
linux kernel
asked 58 mins ago
vincentc
62
New contributor
vincentc 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 |
I wonder how kernel puts data on LLC or L3 caches in detail. I have been searching the information about using cache in kernel but many results talk about page cache or buffered cache but in this question it is only related to cache above the main memory.
Assume that I make a working set or data structure (30MB) in the kernel context by using kmalloc, vmalloc or whatever. What I am thinking is that there might be a different procedure such as protection or extra optimization to prevent any memory violation in kernel unlike using malloc or mmap in user context.
Therefore, if I make a same-size working set(30MB) using user library(malloc) in user mode, I would expect that I might get different performance when I access this data in the working set.
Question
1. How kernel uses LLC cache?
2. Can I get different performance when I allocate memory using malloc?
Any comments or materials would be appreciated :)
linux kernel
asked 58 mins ago
vincentc
62
New contributor
vincentc is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
I wonder how kernel puts data on LLC or L3 caches in detail. I have been searching the information about using cache in kernel but many results talk about page cache or buffered cache but in this question it is only related to cache above the main memory.
Assume that I make a working set or data structure (30MB) in the kernel context by using kmalloc, vmalloc or whatever. What I am thinking is that there might be a different procedure such as protection or extra optimization to prevent any memory violation in kernel unlike using malloc or mmap in user context.
Therefore, if I make a same-size working set(30MB) using user library(malloc) in user mode, I would expect that I might get different performance when I access this data in the working set.
Question
1. How kernel uses LLC cache?
2. Can I get different performance when I allocate memory using malloc?
Any comments or materials would be appreciated :)
linux kernel
linux kernel
asked 58 mins ago
vincentc
62
New contributor
vincentc is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 58 mins ago
vincentc
62
New contributor
vincentc is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 58 mins ago
vincentc
62
New contributor
vincentc is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 58 mins ago
vincentc
62
asked 58 mins ago
vincentc
62
62
New contributor
vincentc is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
vincentc is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
vincentc is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
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1 Answer
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LLC means only "last level cache". It is strongly architecture-dependent, exactly which level of cache is it. In recent x86/amd64 architectures, it is typically L3 cache.
Caching happens mostly independently from the kernel. There is none to little function to manipulate CPU-memory caching, including L3 cache, even on the asm level. It might be dubious, if it is even the task of the kernel to deal with it.
The kernel API doesn't have a malloc() function. It has kmalloc(), which is essentially a malloc(). It has also vmalloc(), which allocates always pages and not bytes.
There are various optimizations in the kernel algorithms to make it better tuned in a caching environment, although they deal mainly with lower cache levels (for example, it is better if concurrent processes/kernel threads work least possible on the same page or cache line).
The kernel is written mainly in C, it handles memory addresses and caching is handled by the cpu memory handler mechanism transparently.
answered 28 mins ago
peterh
4,29092957
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1 Answer
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1 Answer
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active
oldest
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active
oldest
votes
active
oldest
votes
LLC means only "last level cache". It is strongly architecture-dependent, exactly which level of cache is it. In recent x86/amd64 architectures, it is typically L3 cache.
Caching happens mostly independently from the kernel. There is none to little function to manipulate CPU-memory caching, including L3 cache, even on the asm level. It might be dubious, if it is even the task of the kernel to deal with it.
The kernel API doesn't have a malloc() function. It has kmalloc(), which is essentially a malloc(). It has also vmalloc(), which allocates always pages and not bytes.
There are various optimizations in the kernel algorithms to make it better tuned in a caching environment, although they deal mainly with lower cache levels (for example, it is better if concurrent processes/kernel threads work least possible on the same page or cache line).
The kernel is written mainly in C, it handles memory addresses and caching is handled by the cpu memory handler mechanism transparently.
answered 28 mins ago
peterh
4,29092957
add a comment |
LLC means only "last level cache". It is strongly architecture-dependent, exactly which level of cache is it. In recent x86/amd64 architectures, it is typically L3 cache.
Caching happens mostly independently from the kernel. There is none to little function to manipulate CPU-memory caching, including L3 cache, even on the asm level. It might be dubious, if it is even the task of the kernel to deal with it.
The kernel API doesn't have a malloc() function. It has kmalloc(), which is essentially a malloc(). It has also vmalloc(), which allocates always pages and not bytes.
There are various optimizations in the kernel algorithms to make it better tuned in a caching environment, although they deal mainly with lower cache levels (for example, it is better if concurrent processes/kernel threads work least possible on the same page or cache line).
The kernel is written mainly in C, it handles memory addresses and caching is handled by the cpu memory handler mechanism transparently.
answered 28 mins ago
peterh
4,29092957
add a comment |
LLC means only "last level cache". It is strongly architecture-dependent, exactly which level of cache is it. In recent x86/amd64 architectures, it is typically L3 cache.
Caching happens mostly independently from the kernel. There is none to little function to manipulate CPU-memory caching, including L3 cache, even on the asm level. It might be dubious, if it is even the task of the kernel to deal with it.
The kernel API doesn't have a malloc() function. It has kmalloc(), which is essentially a malloc(). It has also vmalloc(), which allocates always pages and not bytes.
There are various optimizations in the kernel algorithms to make it better tuned in a caching environment, although they deal mainly with lower cache levels (for example, it is better if concurrent processes/kernel threads work least possible on the same page or cache line).
The kernel is written mainly in C, it handles memory addresses and caching is handled by the cpu memory handler mechanism transparently.
answered 28 mins ago
peterh
4,29092957
LLC means only "last level cache". It is strongly architecture-dependent, exactly which level of cache is it. In recent x86/amd64 architectures, it is typically L3 cache.
Caching happens mostly independently from the kernel. There is none to little function to manipulate CPU-memory caching, including L3 cache, even on the asm level. It might be dubious, if it is even the task of the kernel to deal with it.
The kernel API doesn't have a malloc() function. It has kmalloc(), which is essentially a malloc(). It has also vmalloc(), which allocates always pages and not bytes.
There are various optimizations in the kernel algorithms to make it better tuned in a caching environment, although they deal mainly with lower cache levels (for example, it is better if concurrent processes/kernel threads work least possible on the same page or cache line).
The kernel is written mainly in C, it handles memory addresses and caching is handled by the cpu memory handler mechanism transparently.
answered 28 mins ago
peterh
4,29092957
answered 28 mins ago
peterh
4,29092957
answered 28 mins ago
peterh
4,29092957
answered 28 mins ago
peterh
4,29092957
4,29092957
add a comment |
add a comment |
vincentc is a new contributor. Be nice, and check out our Code of Conduct.
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