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    SubjectRe: [PATCH bisected regression] sched: rebuild sched domains at suspend/resume
    On 03/07/2012 02:15 AM, Konstantin Khlebnikov wrote:

    > This is fix for suspend/resume regression introduced in commit 8f2f748b0656
    > ("CPU hotplug, cpusets, suspend: Don't touch cpusets during suspend/resume")
    > Without this patch suspend always hangs on my thinkpad x220 (2 x CPU * HT).

    Hey, with commit 8f2f748b0656, suspend/resume works perfectly for me! I ran it
    multiple times just to make sure, and everything worked just great.

    Apart from that, I even tried suspend/resume after building the kernel with
    and without CONFIG_CPUSETS. Both cases worked perfectly.

    So, I am really surprised at what you stated above. Are you *really* sure you
    are facing suspend hangs *because* of the above commit?

    And AFAICS hardware doesn't matter for the code in question, but in any case,
    the laptop on which I tested it is:
    Thinkpad T420 (Intel core i5-2540M), 2 cores * HT (total 4 logical cpus).

    Also, the patch you posted here doesn't make much sense.. nor does it give a
    clue as to what might be wrong at your end (if anything is really wrong, that
    is). Do you have CONFIG_CPUSETS set or unset? Could you share your .config?

    Coming to your patch, assuming you have CONFIG_CPUSETS enabled, then,
    calling rebuild_sched_domains() at that point is useless because the cpusets
    weren't changed at all. So generate_sched_domains() would generate the same
    sched domain partitions that is already there.. And hence
    partition_sched_domains() would essentially do nothing.. no sched domain is
    destroyed, and no new domains are created.

    However, if CONFIG_CPUSETS is unset, then, before commit 8f2f748b0656,
    partition_sched_domains(1, NULL, NULL) would have been invoked, thus rebuilding
    a single sched domain. And that is why I specifically also tested commit
    8f2f748b0656 with CONFIG_CPUSETS unset - and that also worked fine (as I
    mentioned above).

    So could you please check again?

    By the way, you can use the pm-test framework (see Documentation/power/basic-
    pm-debugging.txt) to pin-point which stage is causing the hang.
    Specifically, the stage where CPU hotplug is done is 'processors'.

    So you should probably try out this level:
    # echo processors > /sys/power/pm_test
    # echo mem > /sys/power/state

    Replacing processors with core enables even deeper level suspend testing.

    > cpuset_update_active_cpus() not only juggles with bits in cpusets,
    > it also calls sched-domains rebuilding after all.
    > This patch restores sched-domain rebuilds, as it was before that commit.
    > Signed-off-by: Konstantin Khlebnikov <>
    > ---
    > kernel/sched/core.c | 7 +++++++
    > 1 files changed, 7 insertions(+), 0 deletions(-)
    > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
    > index 9995eb0..0fb7406 100644
    > --- a/kernel/sched/core.c
    > +++ b/kernel/sched/core.c
    > @@ -6732,6 +6732,10 @@ static int cpuset_cpu_active(struct notifier_block *nfb, unsigned long action,
    > case CPU_DOWN_FAILED:
    > cpuset_update_active_cpus();
    > return NOTIFY_OK;
    > + case CPU_ONLINE_FROZEN:
    > + rebuild_sched_domains();
    > + return NOTIFY_OK;
    > default:
    > return NOTIFY_DONE;
    > }
    > @@ -6744,6 +6748,9 @@ static int cpuset_cpu_inactive(struct notifier_block *nfb, unsigned long action,
    > case CPU_DOWN_PREPARE:
    > cpuset_update_active_cpus();
    > return NOTIFY_OK;
    > + rebuild_sched_domains();
    > + return NOTIFY_OK;
    > default:
    > return NOTIFY_DONE;
    > }

    Srivatsa S. Bhat
    IBM Linux Technology Center

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