From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mathieu Desnoyers Subject: Re: [regression] cpuset: offlined CPUs removed from affinity masks Date: Wed, 19 Feb 2020 10:43:05 -0500 (EST) Message-ID: <1589496945.670.1582126985824.JavaMail.zimbra@efficios.com> References: <1251528473.590671.1579196495905.JavaMail.zimbra@efficios.com> <1317969050.4131.1581955387909.JavaMail.zimbra@efficios.com> <20200219151922.GB698990@mtj.thefacebook.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com DB6D92492E5 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efficios.com; s=default; t=1582126985; bh=F+/vdu5pAZWzqj4UTYnyy130uOCt0HluNqHg8+kURaY=; h=Date:From:To:Message-ID:MIME-Version; b=Dn2LM6/Ip3rOfbochDsUS8wZ5WDY0vgo8z2AYSbk/UEtRPEdKAKNZalD9xkxRRKGG xIebRmZTqKeFBhD85KZF1HIZiyhw8M1zvsluupHf9evznni7VJGHnht76y6JiVzKBw aVeHKq0QBG3vlSIr135Dxuw2yJ9NWPZGdyQHVrhEkbzkPtmlTDJvv1oST5+iqQmeJG rLerfJviGIxtX950z4ZjIIpnXx+FmMvnrM681XsDw8GjLPtPdqVbKDwlJskZzxmSHX B2eVbOHejv+y3bffPOgPUo5mG3tpIfgTsGybTSCitYBycMIYwRWulrVAimntrIU3qP MiiBdphPSe9bA== In-Reply-To: <20200219151922.GB698990-146+VewaZzwNjtGbbfXrCEEOCMrvLtNR@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" To: Tejun Heo Cc: Li Zefan , cgroups , linux-kernel , Peter Zijlstra , Ingo Molnar , Valentin Schneider ----- On Feb 19, 2020, at 10:19 AM, Tejun Heo tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org wrote: > Hello, > > On Mon, Feb 17, 2020 at 11:03:07AM -0500, Mathieu Desnoyers wrote: >> Hi, >> >> Adding Tejun and the cgroups mailing list in CC for this cpuset regression I >> reported last month. >> >> Thanks, >> >> Mathieu >> >> ----- On Jan 16, 2020, at 12:41 PM, Mathieu Desnoyers >> mathieu.desnoyers-vg+e7yoeK/dWk0Htik3J/w@public.gmane.org wrote: >> >> > Hi, >> > >> > I noticed the following regression with CONFIG_CPUSET=y. Note that >> > I am not using cpusets at all (only using the root cpuset I'm given >> > at boot), it's just configured in. I am currently working on a 5.2.5 >> > kernel. I am simply combining use of taskset(1) (setting the affinity >> > mask of a process) and cpu hotplug. The result is that with >> > CONFIG_CPUSET=y, setting the affinity mask including an offline CPU number >> > don't keep that CPU in the affinity mask, and it is never put back when the >> > CPU comes back online. CONFIG_CPUSET=n behaves as expected, and puts back >> > the CPU into the affinity mask reported to user-space when it comes back >> > online. > > Because cpuset operations irreversibly change task affinity masks > rather than masking them dynamically, the interaction has always been > kinda broken. Hmm... Are there older kernel vesions which behave > differently? Off the top of my head, I can't think of sth which could > have changed that behavior recently but I could easily be missing > something. Hi Tejun, The regression I'm talking about here is that CONFIG_CPUSET=y changes the behavior of the sched_setaffinify system call, which existed prior to cpusets. sched_setaffinity should behave in the same way for kernels configured with CONFIG_CPUSET=y or CONFIG_CPUSET=n. The fact that cpuset decides to irreversibly change the task affinity mask may not be considered a regression if it has always done that, but changing the behavior of sched_setaffinity seems to fit the definition of a regression. Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com