Messages in this thread | | | Subject | Re: [PATCH v4 1/2] x86/fpu: track AVX-512 usage of tasks | From | Tim Chen <> | Date | Tue, 11 Dec 2018 09:52:43 -0800 |
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On 12/11/18 9:18 AM, 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? >
The reason why I believe that an exponential decay average, or some other kind of weighted decay of the AVX512 usage is better.
Tim
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