Messages in this thread | | | Date | Wed, 19 Oct 2022 12:43:57 +0100 | From | Qais Yousef <> | Subject | Re: [RFC PATCH 00/11] Reviving the Proxy Execution Series |
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On 10/17/22 02:23, Joel Fernandes wrote:
> I ran a test to check CFS time sharing. The accounting on top is confusing, > but ftrace confirms the proxying happening. > > Task A - pid 122 > Task B - pid 123 > Task C - pid 121 > Task D - pid 124 > > Here D and B just spin all the time. C is lock owner (in-kernel mutex) and > spins all the time, while A blocks on the same in-kernel mutex and remains > blocked. > > Then I did "top -H" while the test was running which gives below output. > The first column is PID, and the third-last column is CPU percentage. > > Without PE: > 121 root 20 0 99496 4 0 R 33.6 0.0 0:02.76 t (task C) > 123 root 20 0 99496 4 0 R 33.2 0.0 0:02.75 t (task B) > 124 root 20 0 99496 4 0 R 33.2 0.0 0:02.75 t (task D) > > With PE: > PID > 122 root 20 0 99496 4 0 D 25.3 0.0 0:22.21 t (task A) > 121 root 20 0 99496 4 0 R 25.0 0.0 0:22.20 t (task C) > 123 root 20 0 99496 4 0 R 25.0 0.0 0:22.20 t (task B) > 124 root 20 0 99496 4 0 R 25.0 0.0 0:22.20 t (task D) > > With PE, I was expecting 2 threads with 25% and 1 thread with 50%. Instead I > get 4 threads with 25% in the top. Ftrace confirms that the D-state task is > in fact not running and proxying to the owner task so everything seems > working correctly, but the accounting seems confusing, as in, it is confusing > to see the D-state task task taking 25% CPU when it is obviously "sleeping". > > Yeah, yeah, I know D is proxying for C (while being in the uninterruptible > sleep state), so may be it is OK then, but I did want to bring this up :-)
I seem to remember Valentin raised similar issue about how userspace view can get confusing/misleading:
https://www.youtube.com/watch?v=UQNOT20aCEg&t=3h21m41s
Cheers
-- Qais Yousef
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