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    SubjectRe: [RFC PATCH] cpuacct: per-cgroup utime/stime statistics - v1
    On Wed, 11 Mar 2009 21:04:34 +0530
    Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
    > > > This patch adds a new file cpuacct.stat which displays two stats:
    > > > utime and stime. I wasn't too sure about the usefulness of providing
    > > > per-cgroup guest and steal times and hence not including them here.
    > > >
    > > > Note that I am using percpu_counter for collecting these two stats.
    > > > Since percpu_counter subsystem doesn't protect the readside, readers could
    > > > theoritically obtain incorrect values for these stats on 32bit systems.
    > >
    > > Using percpu_counter_read() means that .. but is it okay to ignore "batch"
    > > number ? (see FBC_BATCH)
    > >
    >
    > FBC_BATCH? Thats gone..no? We have dynamic batches now, IIRC. Could
    > you please elaborate on your comment?
    >
    Ah, ok. it's now extern int percpu_counter_batch.

    -Kame

    > >
    > > > I hope occasional wrong values is not too much of a concern for
    > > > statistics like this. If it is a problem, we have to either fix
    > > > percpu_counter or do it all by ourselves as Kamezawa attempted
    > > > for cpuacct.usage (http://lkml.org/lkml/2009/3/4/14)
    > > >
    > > Hmm, percpu_counter_sum() is bad ?
    > >
    >
    > Yes, but we need to sum somewhere.. user space summing will not be
    > atomic, we'll get several snapshots of per CPU data and summing it
    > might not yield the correct answers.
    >
    > > BTW, I'm not sure but don't we need special handling if
    > > CONFIG_VIRT_CPU_ACCOUNTING=y ?
    >
    > Good point. Bharata, with CONFIG_VIRT_CPU_ACCOUNTING, utime and stime
    > is accounted for within the architecture.
    >
    > --
    > Balbir
    > --
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