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SubjectRe: Attaching a process to cgroups
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On Thu, 2012-07-26 at 17:02 +0400, Alexey Vlasov wrote: 
> On Wed, Jul 25, 2012 at 03:57:47PM +0200, Mike Galbraith wrote:
> >
> > I'd profile it with perf, and expect to find a large pile of cycles.
>
> I did it the as following:
> # perf stat cat /proc/self/cgroup
>
> 4:blkio:/
> 3:devices:/
> 2:memory:/
> 1:cpuacct:/
>
> Performance counter stats for 'cat /proc/self/cgroup':
>
> 0.472513 task-clock # 0.000 CPUs utilized
> 1 context-switches # 0.002 M/sec
> 1 CPU-migrations # 0.002 M/sec
> 169 page-faults # 0.358 M/sec
> 1111521 cycles # 2.352 GHz
> 784737 stalled-cycles-frontend # 70.60% frontend cycles idle
> 445520 stalled-cycles-backend # 40.08% backend cycles idle
> 576622 instructions # 0.52 insns per cycle
> # 1.36 stalled cycles per insn
> 120032 branches # 254.029 M/sec
> 6577 branch-misses # 5.48% of all branches
>
> 9.114631804 seconds time elapsed

Sleepy box.

> # perf report --sort comm,dso

perf report --sort symbol,dso won't toss everything in one basket.

> Kernel address maps (/proc/{kallsyms,modules}) were restricted.
>
> Check /proc/sys/kernel/kptr_restrict before running 'perf record'.
>
> If some relocation was applied (e.g. kexec) symbols may be misresolved.
>
> Samples in kernel modules can't be resolved as well.
>
> # ========
> # captured on: Thu Jul 26 16:23:06 2012
> # hostname : l24
> # os release : 3.3.3-1gb-c-s-m
> # perf version : 3.2
> # arch : x86_64
> # nrcpus online : 24
> # nrcpus avail : 24
> # cpudesc : Intel(R) Xeon(R) CPU E5645 @ 2.40GHz
> # total memory : 74181032 kB
> # cmdline : /usr/sbin/perf record cat /proc/self/cgroup
>
> # event : name = cycles, type = 0, config = 0x0, config1 = 0x0, config2 = 0x0, excl_usr = 0, excl_kern = 0, id = { 1758, 1759, 1760, 1761, 1762, 1763, 1764, 1765, 1766, 1767, 1768, 1769, 1770, 1771, 1772, 1773, 1774, 1775, 1776, 1777, 1778, 1779, 1780, 1781 }
> # HEADER_CPU_TOPOLOGY info available, use -I to display
> # HEADER_NUMA_TOPOLOGY info available, use -I to display
> # ========
> #
> # Events: 21 cycles
> #
> # Overhead Command Shared Object
> # ........ ....... .................
> #
> 100.00% cat [kernel.kallsyms]
>
> but I don't know what next unfortunately.

I'll have to pass. I would just stop creating thousands of cgroups ;-)

They've become a lot more scalable fairly recently, but if you populate
those thousands with frequently runnable tasks, I suspect you'll still
see huge truckloads of scheduler in profiles.. maybe even nothing else.

> I also checked the same thing on the other server with the 2.6.37 kernel,
> there' some thousands cgroups too, and it somehow works there immediately.






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