linux-kernel - Re: [PATCH RFC] sched: Add a per-thread core scheduling interface(Internet mail)

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Message-ID: <20200521134913.GB140701@google.com>
Date:   Thu, 21 May 2020 09:49:13 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     benbjiang(蒋彪) <benbjiang@...cent.com>
Cc:     Nishanth Aravamudan <naravamudan@...italocean.com>,
        Julien Desfossez <jdesfossez@...italocean.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        "mingo@...nel.org" <mingo@...nel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "pjt@...gle.com" <pjt@...gle.com>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        vpillai <vpillai@...italocean.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "fweisbec@...il.com" <fweisbec@...il.com>,
        "keescook@...omium.org" <keescook@...omium.org>,
        "kerrnel@...gle.com" <kerrnel@...gle.com>,
        Phil Auld <pauld@...hat.com>, Aaron Lu <aaron.lwe@...il.com>,
        Aubrey Li <aubrey.intel@...il.com>,
        "aubrey.li@...ux.intel.com" <aubrey.li@...ux.intel.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH RFC] sched: Add a per-thread core scheduling
 interface(Internet mail)

On Thu, May 21, 2020 at 04:09:50AM +0000, benbjiang(蒋彪) wrote:
> 
> 
> > On May 21, 2020, at 6:26 AM, Joel Fernandes (Google) <joel@...lfernandes.org> wrote:
> > 
> > Add a per-thread core scheduling interface which allows a thread to tag
> > itself and enable core scheduling. Based on discussion at OSPM with
> > maintainers, we propose a prctl(2) interface accepting values of 0 or 1.
> > 1 - enable core scheduling for the task.
> > 0 - disable core scheduling for the task.
> > 
> > Special cases:
> > (1)
> > The core-scheduling patchset contains a CGroup interface as well. In
> > order for us to respect users of that interface, we avoid overriding the
> > tag if a task was CGroup-tagged because the task becomes inconsistent
> > with the CGroup tag. Instead return -EBUSY.
> > 
> > (2)
> > If a task is prctl-tagged, allow the CGroup interface to override
> > the task's tag.
> > 
> > ChromeOS will use core-scheduling to securely enable hyperthreading.
> > This cuts down the keypress latency in Google docs from 150ms to 50ms
> > while improving the camera streaming frame rate by ~3%.
> Hi,
> Are the performance improvements compared to the hyperthreading disabled scenario or not?
> Could you help to explain how the keypress latency improvement comes with core-scheduling?

Hi Jiang,

The keypress end-to-end latency metric we have is calculated from when the
keypress is registered in hardware to when a character is drawn on the
scereen. This involves several parties including the GPU and browser
processes which are all running in the same trust domain and benefit from
parallelism through hyperthreading.

thanks,

 - Joel