Messages in this thread | | | Subject | Re: [PATCH v4 1/2] x86/fpu: track AVX-512 usage of tasks | From | Arjan van de Ven <> | Date | Tue, 11 Dec 2018 16:14:19 -0800 |
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On 12/11/2018 3:46 PM, Li, Aubrey wrote: > On 2018/12/12 1:18, Dave Hansen wrote: >> On 12/10/18 4:24 PM, Aubrey Li wrote: >>> The tracking turns on the usage flag at the next context switch of >>> the task, but requires 3 consecutive context switches with no usage >>> to clear it. This decay is required because well-written AVX-512 >>> applications are expected to clear this state when not actively using >>> AVX-512 registers. >> >> One concern about this: Given a HZ=1000 system, this means that the >> flag needs to get scanned every ~3ms. That's a pretty good amount of >> scanning on a system with hundreds or thousands of tasks running around. >> >> How many tasks does this scale to until you're eating up an entire CPU >> or two just scanning /proc? >> > > Do we have a real requirement to do this in practical environment? > AFAIK, 1s or even 5s is good enough in some customers environment.
maybe instead of a 1/0 bit, it's useful to store the timestamp of the last time we found the task to use avx? (need to find a good time unit)
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