[Devel] Re: How to draw values for /proc/stat

[Zhu Yanhai]

2011/12/5 Glauber Costa <glommer at parallels.com>:
> Hi,
>
> Specially Peter and Paul, but all the others:
>
> As you can see in https://lkml.org/lkml/2011/12/4/178, and in my answer to
> that, there is a question - one I've asked before but without that much of
> an audience - of whether /proc files read from process living on cgroups
> should display global or per-cgroup resources.
>
> In the past, I was arguing for a knob to control that, but I recently
> started to believe that a knob here will only overcomplicate matters:
> if you live in a cgroup, you should display only the resources you can
> possibly use. Global is for whoever is in the main cgroup.
>
> Now, it comes two questions:
> 1) Do you agree with that, for files like /proc/stat ? I think the most
> important part is to be consistent inside the system, regardless of what is
> done
>
> 2) Will cpuacct stay? I think if it does, that becomes almost mandatory (at
> least the bind mount idea is pretty much over here), because drawing value
> for /proc/stat becomes quite complex.
> The cpuacct cgroup can provide user, sys, etc values. But we also have:
>
> * nr_context_switches,
> * jiffies since boot,
> * total_forks,
> * nr_running,
> * nr_iowait,
>
> Now I doubt any of us want to see /proc/stat extended to accommodate things
> like nr_context_switches, or even worse, nr_running. The way I see it, there
> are two options here:
>
>  a) moving everything to cpu cgroup so we keep all values being drawn
>    from the same place
>  b) Collect that info from multiple places in a transparent way. ctx,
>    nr_running and nr_iowait will probably come from cpu. jiffies can
>    come from wherever, and maybe we can even draw total_forks
>    from Frederic's and avoid counting it twice.
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Hi,
I think making /proc files read from process living on cgroups display
per-cgroup resources is a good idea, at least from a common user's
perspective. We are (well, we will) setup a large cluster with
lxc/cgroup for some backend online services in the next months, and
one gap we see is the entries under /proc are not virtualized enough,
especially those performance counters, not only schedule counters
(e.g. /proc/diskstat). Although we can read some numbers in the host
from blkio controller's counters like blkio.io_serviced,
blkio.io_service_time etc, it would be very convenient if the entries
under /proc are virtualized, as we can deploy various existing
maintenance tools directly in the containers, without developing
another monitors. So the over-cost for maintenance can be low.

Let's include lxc-user mailing list for this topic.

--
Thanks,
Zhu Yanhai