Messages in this thread | | | Subject | Re: [PATCH v13 2/3] x86,/proc/pid/status: Add AVX-512 usage elapsed time | From | "Li, Aubrey" <> | Date | Sat, 6 Apr 2019 23:41:57 +0800 |
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On 2019/4/6 4:27, Jann Horn wrote: > On Fri, Apr 5, 2019 at 10:02 PM Aubrey Li <aubrey.li@linux.intel.com> wrote: >> AVX-512 components use could cause core turbo frequency drop. So >> it's useful to expose AVX-512 usage elapsed time as a heuristic hint >> for the user space job scheduler to cluster the AVX-512 using tasks >> together. >> >> Tensorflow example: >> $ while [ 1 ]; do cat /proc/pid/status | grep AVX; sleep 1; done >> AVX512_elapsed_ms: 4 >> AVX512_elapsed_ms: 8 >> AVX512_elapsed_ms: 4 >> >> This means that 4 milliseconds have elapsed since the AVX512 usage >> of tensorflow task was detected when the task was scheduled out. >> >> Or: >> $ cat /proc/pid/status | grep AVX512_elapsed_ms >> AVX512_elapsed_ms: -1 > > (Very nitpicky, feel free to ignore: If you change the /proc/pid to > /proc/tid in the commit message, it becomes clearer that this status > is really per-task/thread, not per-process/threadgroup.)
Thanks, I'll refine.
> > [...] >> + >> +/* >> + * Report the amount of time elapsed in millisecond since last AVX512 >> + * use in the task. >> + */ >> +static void avx512_status(struct seq_file *m, struct task_struct *task) >> +{ >> + unsigned long timestamp = task->thread.fpu.avx512_timestamp; > > This is theoretically a data race, right? Should this have a READ_ONCE() on it?
Thanks, I'll refine.
> > Is there something that zeroes out the avx512_timestamp on > fork()/clone(), or will every child inherit the avx512 timestamp? As > far as I can tell, the timestamp is inherited; I think it would be > nicer to zero it out at that point. Either way, It might be worth > documenting this decision. >
This timestamp is not inherited, see below:
_do_fork() ->copy_process() -->dup_task_struct() --->arch_dup_task_struct() ---->fpu__copy()
Thanks, -Aubrey
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