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)
