Messages in this thread | | | Date | Fri, 23 Jan 2015 09:57:05 +0100 | From | Peter Zijlstra <> | Subject | Re: [RFC PATCH] sched, timer: Use atomics for thread_group_cputimer stats |
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On Thu, Jan 22, 2015 at 07:31:53PM -0800, Jason Low wrote: > When 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 the 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%.
I'll have to look; I worry about consistency between the values. But why would any self respecting piece of software use this crap stuff? Its a guaranteed scalability fail.
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