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    SubjectRe: [PATCH 2/3] sched, timer: Use atomics for thread_group_cputimer to improve scalability
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    On Tue, 2015-04-14 at 16:09 -0700, Jason Low wrote:
    > While running a database workload, we found a scalability issue with itimers.
    >
    > Much of the problem was caused by the thread_group_cputimer spinlock.
    > Each time we account for group system/user time, we need to obtain a
    > thread_group_cputimer's spinlock to update the timers. On larger systems
    > (such as a 16 socket machine), this caused more than 30% of total time
    > spent trying to obtain this kernel lock to update these group timer stats.
    >
    > This patch converts the timers to 64 bit atomic variables and use
    > atomic add to update them without a lock. With this patch, the percent
    > of total time spent updating thread group cputimer timers was reduced
    > from 30% down to less than 1%.

    What does 30% less time spent dealing with the thread_group_cputimer's
    spinlock buy us? iow, does this help DB benchmark throughput or such?

    Thanks,
    Davidlohr



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