Subject: Re: [PATCH 1/2] perf_events: add support for per-cpu per-cgroup
 monitoring (v5)
From: Peter Zijlstra <peterz@infradead.org>
To: balbir@linux.vnet.ibm.com
Cc: Li Zefan <lizf@cn.fujitsu.com>, eranian@google.com,
        linux-kernel@vger.kernel.org, mingo@elte.hu, paulus@samba.org,
        davem@davemloft.net, fweisbec@gmail.com, perfmon2-devel@lists.sf.net,
        eranian@gmail.com, robert.richter@amd.com, acme@redhat.com,
        Paul Menage <menage@google.com>, Greg Kroah-Hartman <gregkh@suse.de>
In-Reply-To: <20101126025605.GF3298@balbir.in.ibm.com>
References: <4ce510d4.0fedd80a.742c.10b9@mx.google.com>
	 <1290684523.2145.31.camel@laptop> <4CEF1260.4000009@cn.fujitsu.com>
	 <20101126025605.GF3298@balbir.in.ibm.com>
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Date: Fri, 26 Nov 2010 12:17:36 +0100
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On Fri, 2010-11-26 at 08:26 +0530, Balbir Singh wrote:
> * lizf@cn.fujitsu.com <lizf@cn.fujitsu.com> [2010-11-26 09:50:24]:
> 
> > 19:28, Peter Zijlstra wrote:
> > > On Thu, 2010-11-18 at 12:40 +0200, Stephane Eranian wrote:
> > >> This kernel patch adds the ability to filter monitoring based on
> > >> container groups (cgroups). This is for use in per-cpu mode only.
> > >>     
> > >> The cgroup to monitor is passed as a file descriptor in the pid
> > >> argument to the syscall. The file descriptor must be opened to 
> > >> the cgroup name in the cgroup filesystem. For instance, if the
> > >> cgroup name is foo and cgroupfs is mounted in /cgroup, then the
> > >> file descriptor is opened to /cgroup/foo. Cgroup mode is
> > >> activated by passing PERF_FLAG_PID_CGROUP in the flags argument
> > >> to the syscall.
> > >>
> > >> For instance to measure in cgroup foo on CPU1 assuming
> > >> cgroupfs is mounted under /cgroup:
> > >>
> > >> struct perf_event_attr attr;
> > >> int cgroup_fd, fd;
> > >>
> > >> cgroup_fd = open("/cgroup/foo", O_RDONLY);
> > >> fd = perf_event_open(&attr, cgroup_fd, 1, -1, PERF_FLAG_PID_CGROUP);
> > >> close(cgroup_fd);
> > >>
> > >> Signed-off-by: Stephane Eranian <eranian@google.com> 
> > > 
> > > Could you please split this patch:
> > >   - pure code movement
> > >   - time accounting changes
> > >   - event_filter_match() stuff
> > >   - cgroup thing
> > > 
> > > From a quick reading it doesn't look bad, but I want an ACK from the
> > > cgroup people -- specifically if they're OK with the filedesc juggling
> > > thing, because I know the sysfs people objected to such tricks.
> > > 
> > 
> > Long long ago, a feature that used this trick was accepted, and that's
> > cgroup taskstat.

egads, I  knew I should have looked at that.. :/

> > You get an fd of a cgroup directory and send it to the kernel via netlink,
> > and then you'll receive some statistics, such as how many tasks are
> > running/interrupted in that cgroup.
> >
> 
> That is right, since cgroups don't have id's there is no easy way to
> identify them, looking them up by name and passing strings seemed an
> overkill. 

You could of course have added an ID instead ;-)
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