Hi Zefan, > -----Original Message----- > From: Zefan Li [mailto:lizefan@xxxxxxxxxx] > Sent: Monday, January 04, 2016 9:52 AM > To: Chen, Yu C; cgroups@xxxxxxxxxxxxxxx > Cc: linux-kernel@xxxxxxxxxxxxxxx; Vlastimil Babka; Rik van Riel; Joonsoo Kim; > David Rientjes; Vishnu Pratap Singh; Pintu Kumar; Michal Nazarewicz; Mel > Gorman; Gortmaker, Paul (Wind River); Peter Zijlstra; Tim Chen; Hugh Dickins; > Tejun Heo > Subject: Re: [PATCH] cpuset: fix cpus_allowed mask for offline/online CPUs > > On 2016/1/1 20:09, Chen Yu wrote: > > Commit be4c9dd7aee5 ("cpuset: enable onlined cpu/node in effective > > masks") leverages cpuset's cpus_allowed and its parent's > > effective_cpus to calculate the new_cpus by: > > > > cpumask_and(&new_cpus, cs->cpus_allowed, > > parent_cs(cs)->effective_cpus); > > > > However cpus_allowed will also be updated after the CPU is offline, in > > hotplug_update_tasks_legacy, so when the CPU is online again, it will > > use the old cpus_allowed mask to calculate the new_cpus, thus new_cpus > > will get incorrect value after each round of offline/online. > > > > This problem is found on ubuntu 15.10 with cpuset mounted: > > > > 1. echo 0 > /sys/devices/system/cpu/cpu2/online > > 2. echo 1 > /sys/devices/system/cpu/cpu2/online > > 3. cat /sys/fs/cgroup/cpuset/cpuset.cpus > > 0-3 > > 4. cat /sys/fs/cgroup/cpuset/user.slice/cpuset.cpus > > 0-1,3 > > 5. taskset -c 2 ls > > taskset: failed to set pid 0's affinity: Invalid argument > > > > This is the expected behavior...In legacy hierachy onlining an offlined cpu > won't restore cpuset configurations automatically. [Yu] Ah, I see, we were just a little confused with it before. So if we want to online an offlined cpu in legacy hierarchy, we should not only echo 1 to 'online' sysfs, but also restore the mask manually? It seems that we should not rely on /sys/devices/system/cpu/cpu2/online, if cpuset has been mounted. > > Commit be4c9dd7aee5 changed this behavior, but only for unified hierachy. thanks, yu -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
