linux-kernel - Re: [PATCH 0/7] sched/deadline: fix cpusets bandwidth accounting

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Message-ID: <20170825163754.08bda23f@luca>
Date:   Fri, 25 Aug 2017 16:37:54 +0200
From:   Luca Abeni <luca.abeni@...tannapisa.it>
To:     Mathieu Poirier <mathieu.poirier@...aro.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>, tj@...nel.org,
        vbabka@...e.cz, Li Zefan <lizefan@...wei.com>,
        akpm@...ux-foundation.org, weiyongjun1@...wei.com,
        Juri Lelli <juri.lelli@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Claudio Scordino <claudio@...dence.eu.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Tommaso Cucinotta <tommaso.cucinotta@...up.it>
Subject: Re: [PATCH 0/7] sched/deadline: fix cpusets bandwidth accounting

Hi Mathieu,

On Wed, 23 Aug 2017 13:47:13 -0600
Mathieu Poirier <mathieu.poirier@...aro.org> wrote:

> On 22 August 2017 at 06:21, Luca Abeni <luca.abeni@...tannapisa.it> wrote:
> > Hi Mathieu,  
> 
> Good day to you,
> 
> >
> > On Wed, 16 Aug 2017 15:20:36 -0600
> > Mathieu Poirier <mathieu.poirier@...aro.org> wrote:
> >  
> >> This is a renewed attempt at fixing a problem reported by Steve Rostedt [1]
> >> where DL bandwidth accounting is not recomputed after CPUset and CPUhotplug
> >> operations.  When CPUhotplug and some CUPset manipulation take place root
> >> domains are destroyed and new ones created, loosing at the same time DL
> >> accounting pertaining to utilisation.  
> >
> > Thanks for looking at this longstanding issue! I am just back from
> > vacations; in the next days I'll try your patches.
> > Do you have some kind of scripts for reproducing the issue
> > automatically? (I see that in the original email Steven described how
> > to reproduce it manually; I just wonder if anyone already scripted the
> > test).  
> 
> I didn't bother scripting it since it is so easy to do.  I'm eager to
> see how things work out on your end.

I ran some tests with your patchset, and I confirm that it fixes the
issue originally pointed out by Steven.

But I still need to run some more tests (I'll continue on Monday).

I think I found an issue by:
1) creating two disjoint cpusets (CPUs 0 and 1 in the first cpuset,
   CPUs 2 and 3 in the second one) and setting sched_load_balance to 0
2) starting a task in one of the two cpusets, and making it
   SCHED_DEADLINE <--- up to here, everything looks fine
3) setting sched_load_balance to 1 <--- At this point, I think there is
   a bug: the system has only one root domain, and the task utilization
   is summed to it... But the task affinity mask is still the one of
   the "old root domain" that was associated with the cpuset where the
   task is executing.

I still need to run some experiments about this.



				Thanks,
					Luca