Messages in this thread | | | Date | Mon, 18 Jul 2016 16:50:24 -0400 | From | Waiman Long <> | Subject | Re: [PATCH v3 0/3] locking/mutex: Enable optimistic spinning of lock waiter |
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On 07/18/2016 01:59 PM, Jason Low wrote: > On Tue, 2016-03-22 at 13:46 -0400, Waiman Long wrote: >> v2->v3: >> - Remove patch 4 as it is not useful. >> - Allow need_resched() check for waiter& add more comments about >> changes to address issues raised by PeterZ. >> >> v1->v2: >> - Set task state to running before doing optimistic spinning. >> - Add 2 more patches to handle possible missed wakeups and wasteful >> spinning in try_to_wake_up() function. >> >> This patchset is a variant of PeterZ's "locking/mutex: Avoid spinner >> vs waiter starvation" patch. The major difference is that the >> waiter-spinner won't enter into the OSQ used by the spinners. Instead, >> it will spin directly on the lock in parallel with the queue head >> of the OSQ. So there will be a bit more cacheline contention on the >> lock cacheline, but that shouldn't cause noticeable impact on system >> performance. >> >> This patchset tries to address 2 issues with Peter's patch: >> >> 1) Ding Tianhong still find that hanging task could happen in some cases. >> 2) Jason Low found that there was performance regression for some AIM7 >> workloads. >> >> By making the waiter-spinner to spin directly on the mutex, it will >> increase the chance for the waiter-spinner to get the lock instead >> of waiting in the OSQ for its turn. >> >> Patch 1 modifies the mutex_optimistic_spin() function to enable it >> to be called by a waiter-spinner that doesn't need to go into the OSQ. >> >> Patch 2 modifies the mutex locking slowpath to make the waiter call >> mutex_optimistic_spin() to do spinning after being waken up. > Just in case, here was the Waiman's patch that I was referring to for > addressing some of the starvation issues with mutex by allowing the > waiter to do optimistic spinning after being woken up. > >> Patch 3 reverses the sequence of setting task state and changing >> mutex count to -1 to prevent the possibility of missed wakeup. >> >> Patch 4 modifies the wakeup code to abandon the wakeup operation >> while spinning on the on_cpu flag if the task has changed back to a >> non-sleeping state. >> >> My own test on a 4-socket E7-4820 v3 system showed a regression of >> about 4% in the high_systime workload with Peter's patch which this >> new patch effectively eliminates. >> >> Testing on an 8-socket Westmere-EX server, however, has performance >> change from -9% to than +140% on the fserver workload of AIM7 >> depending on how the system was set up. >> >> Waiman Long (3): >> locking/mutex: Add waiter parameter to mutex_optimistic_spin() >> locking/mutex: Enable optimistic spinning of woken task in wait queue >> locking/mutex: Avoid missed wakeup of mutex waiter >> >> kernel/locking/mutex.c | 126 ++++++++++++++++++++++++++++++++++-------------- >> 1 files changed, 90 insertions(+), 36 deletions(-)
I have just sent out an updated patchset to address this issue.
Cheers, Longman
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