Re: [benchmark] 1% performance overhead of paravirt_ops on nativekernels

[Ingo Molnar]

* Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:

> I was benchmarking btrfs on my little EeePC. There, kmap overhead 
> was 25% of file access time. Part of it is that people have been 
> taught to use "kmap_atomic()", which is usable under spinlocks and 
> people have been told that it's "fast". It's not fast. The whole 
> TLB thing is slow as hell.

yeah. I noticed it some time ago that INVLPG is unreasonably slow.

My theory is that in the CPU it's perhaps a loop (in microcode?) 
over _all_ TLBs - so as TLB caches get larger, INVLPG gets slower 
and slower ...

	Ingo
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