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Date: Mon, 4 Jan 2016 10:20:35 +0800 From: Zefan Li <lizefan@...wei.com> To: "Chen, Yu C" <yu.c.chen@...el.com>, "cgroups@...r.kernel.org" <cgroups@...r.kernel.org> CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "Vlastimil Babka" <vbabka@...e.cz>, Rik van Riel <riel@...hat.com>, Joonsoo Kim <iamjoonsoo.kim@....com>, David Rientjes <rientjes@...gle.com>, "Vishnu Pratap Singh" <vishnu.ps@...sung.com>, Pintu Kumar <pintu.k@...sung.com>, "Michal Nazarewicz" <mina86@...a86.com>, Mel Gorman <mgorman@...e.de>, "Gortmaker, Paul (Wind River)" <paul.gortmaker@...driver.com>, Peter Zijlstra <peterz@...radead.org>, Tim Chen <tim.c.chen@...ux.intel.com>, Hugh Dickins <hughd@...gle.com>, Tejun Heo <tj@...nel.org> 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? Right. You have to take care of this by yourself. > It seems that we should not rely on /sys/devices/system/cpu/cpu2/online, > if cpuset has been mounted. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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