(switched to email. Please respond via emailed reply-to-all, not via the bugzilla web interface). sched suckage! Do we have a linear search in there? On Mon, 19 Jul 2010 14:38:09 GMT bugzilla-daemon@xxxxxxxxxxxxxxxxxxx wrote: > https://bugzilla.kernel.org/show_bug.cgi?id=16417 > > Summary: Slow context switches with SMP and > CONFIG_FAIR_GROUP_SCHED > Product: Process Management > Version: 2.5 > Kernel Version: 2.6.34.1 > Platform: All > OS/Version: Linux > Tree: Mainline > Status: NEW > Severity: normal > Priority: P1 > Component: Scheduler > AssignedTo: mingo@xxxxxxx > ReportedBy: pbourdon@xxxxxxxxxxxxx > Regression: No > > > Hello, > > We have been experiencing slow context switches using a large number of cgroups > (around 600 groups) and CONFIG_FAIR_GROUP_SCHED. This causes a system time > usage increase on context switching heavy processes (measured with pidstat -w) > and a drop in timer interrupts handling. > > This problem only appears on SMP : when booting with nosmp, the issue does not > appear. From maxprocs=2 to maxprocs=8 we were able to reproduce it accurately. > > Steps to reproduce : > - mount the cgroup filesystem in /dev/cgroup > - cd /dev/cgroup && for i in $(seq 1 5000); do mkdir test_group_$i; done > - launch lat_ctx from lmbench, for instance ./lat_ctx -N 200 100 > > The results from lat_ctx were the following : > - SMP enabled, no cgroups : 2.65 > - SMP enabled, 1000 cgroups : 3.40 > - SMP enabled, 6000 cgroups : 3957.36 > - SMP disabled, 6000 cgroups : 1.58 > > We can see that from a certain amount of cgroups, the context switching starts > taking a lot of time. Another way to reproduce this problem : > - launch cat /dev/zero | pv -L 1G > /dev/null > - look at the CPU usage (about 40% here) > - cd /dev/cgroup && for i in $(seq 1 5000); do mkdir test_group_$i; done > - look at the CPU usage (about 80% here) > > Also note that when a lot of cgroups are present, the system is spending a lot > of time in softirqs, and there are less timer interrupts handled than normally > (according to our graphs). > _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
