linux-kernel - Re: [RFC PATCH v1 2/2] proc: add /proc/<pid>/thread

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Message-ID: <20181112085650.GM3056@worktop>
Date:   Mon, 12 Nov 2018 09:56:50 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Aubrey Li <aubrey.li@...el.com>, tglx@...utronix.de,
        mingo@...hat.com, hpa@...or.com, ak@...ux.intel.com,
        tim.c.chen@...ux.intel.com, arjan@...ux.intel.com,
        linux-kernel@...r.kernel.org, Aubrey Li <aubrey.li@...ux.intel.com>
Subject: Re: [RFC PATCH v1 2/2] proc: add /proc/<pid>/thread_state

On Mon, Nov 12, 2018 at 06:31:47AM +0100, Ingo Molnar wrote:
> 
> * Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Thu, Nov 08, 2018 at 07:32:46AM +0100, Ingo Molnar wrote:
> > > 
> > > * Aubrey Li <aubrey.li@...el.com> wrote:
> > > 
> > > > Expose the per-task cpu specific thread state value, it's helpful
> > > > for userland to classify and schedule the tasks by different policies
> > > 
> > > That's pretty vague - what exactly would use this information? I'm sure 
> > > you have a usecase in mind - could you please describe it?
> > 
> > Yeah, "thread_state" is a pretty terrible name for this. The use-case is
> > detectoring which tasks use AVX3 such that a userspace component (think
> > job scheduler) can cluster them together.
> 
> I'd prefer the kernel to do such clustering...

I think that is a next step.

Also, while the kernel can do this at a best effort basis, it cannot
take into account things the kernel doesn't know about, like high
priority job peak load etc.., things a job scheduler would know.

Then again, a job scheduler would likely already know about the AVX
state anyway.