CODEWITHSUNDEEP
clinuxperformancecaching
Mike
Mike

Reputation: 1871

Run a program without cache

We always talks about how to better use cache to speed up the program. However, if I have a background program, which is not latency-sensitive. I also have some latency-sensitive program running on the same computer. In order to avoid the background program pollute the cache of the latency-sensitive program, I have two choices:

1) Use page-color or some other techniques to "partition" cache and let the latency-sensitive program run in several cache colors, while background programs never uses the memory with those cache colors. <-- I know how this works and have no question on this approach.

2) Can we just mark the memory used by the background program as not-cachable? In other words, all of the memory access from the background program will by-pass the cache so that the cache won't be polluted?

I know we could bypass al of the cache on the machine by setting the 30th bit of CR3 register. But how can we just make some programs by-pass the cache while the others programs still use cache?

[ADD A QUESTION] Is it possible to mark a memory page bypass the cache? In other words, can we mark a memory page not cachable?

Thank you very much for your insight!

Upvotes: 2

Views: 618

Answers (1)

Hadi Brais
Hadi Brais

Reputation: 23639

You can use the Memory Type Range Registers (MTRRs) and/or Page Attribute Table (PAT) features of modern x86 processors. You can use these features to mark certain regions of memory as uncacheable. In particular, you can use the UC, UC-, or WC memory types. But you'll have to know which regions of memory are used by the latency-insensitive application. For more information, refer to the Intel manual Volume 3 Chapter 11: Memory Cache Control.

The closest thing you can do in user mode is by using non-temporal accesses (NTAs).

I know we could bypass al of the cache on the machine by setting the 30th bit of CR3 register.

I think you mean bit 30 of CR0, not CR3.

Upvotes: 1

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