Messages in this thread | | | Date | Tue, 11 Dec 2018 09:53:52 -0800 | From | Andi Kleen <> | Subject | Re: [PATCH v4 1/2] x86/fpu: track AVX-512 usage of tasks |
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On Tue, Dec 11, 2018 at 09:18:25AM -0800, 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?
Yes that's why we may need to propagate it to cgroups in the kernel, because user daemons don't really want to track every TID.
But per pid is a start so that people can start experimenting with this.
Then with some experience fancier interfaces for it can be implemented.
-Andi
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