lkml.org 
[lkml]   [2018]   [Dec]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH v4 1/2] x86/fpu: track AVX-512 usage of tasks
From
Date
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)

\
 
 \ /
  Last update: 2018-12-12 01:15    [W:0.058 / U:0.164 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site