----- On Feb 19, 2020, at 10:19 AM, Tejun Heo tj@xxxxxxxxxx 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@xxxxxxxxxxxx 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
