linux-kernel - Re: [PATCH v2] sched/core: Don't mix isolcpus and housekeeping CPUs

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Message-Id: <20181024104124.GC18466@linux.vnet.ibm.com>
Date:   Wed, 24 Oct 2018 16:11:24 +0530
From:   Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Mel Gorman <mgorman@...hsingularity.net>,
        Ingo Molnar <mingo@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Rik van Riel <riel@...riel.com>,
        Yi Wang <wang.yi59@....com.cn>, zhong.weidong@....com.cn,
        Yi Liu <liu.yi24@....com.cn>,
        Frederic Weisbecker <frederic@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2] sched/core: Don't mix isolcpus and housekeeping CPUs

* Peter Zijlstra <peterz@...radead.org> [2018-10-24 12:15:08]:

> On Wed, Oct 24, 2018 at 03:16:46PM +0530, Srikar Dronamraju wrote:
> > * Mel Gorman <mgorman@...hsingularity.net> [2018-10-24 09:56:36]:
> > 
> > > On Wed, Oct 24, 2018 at 08:32:49AM +0530, Srikar Dronamraju wrote:
> > > It would certainly be a bit odd because the
> > > application is asking for some protection but no guarantees are given
> > > and the application is not made aware via an error code that there is a
> > > problem. Asking the application to parse dmesg hoping to find the right
> > > error message is going to be fragile.
> > 
> > Its a actually a good question.
> > What should we be doing if a mix of isolcpus and housekeeping (aka
> > non-isolcpus) is given in the mask.
> > 
> > Right now as you pointed, there is no easy way for the application to know
> > which are the non-isolcpus to set its affinity. cpusets effective_cpus and
> > cpus_allowed both will contain isolcpus too.
> 
> The easy option is to not use isolcpus :-) It is a horrifically bad
> interface.

Agree, but thats something thats been exposed long time back.
Do we have an option to remove that?  Hopefully nobody is using it.

-- 
Thanks and Regards
Srikar Dronamraju