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Groups > linux.kernel > #1423252
| From | Peter Zijlstra <peterz@infradead.org> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [RFC PATCH-tip v2 2/6] locking/rwsem: Stop active read lock ASAP |
| Date | 2016-06-15 19:30 +0200 |
| Message-ID | <rKmNz-5ul-17@gated-at.bofh.it> (permalink) |
| References | <rK5jH-2zl-5@gated-at.bofh.it> <rK5to-2E2-31@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On Tue, Jun 14, 2016 at 06:48:05PM -0400, Waiman Long wrote: > Currently, when down_read() fails, the active read locking isn't undone > until the rwsem_down_read_failed() function grabs the wait_lock. If the > wait_lock is contended, it may takes a while to get the lock. During > that period, writer lock stealing will be disabled because of the > active read lock. > > This patch will release the active read lock ASAP so that writer lock > stealing can happen sooner. The only downside is when the reader is > the first one in the wait queue as it has to issue another atomic > operation to update the count. > > On a 4-socket Haswell machine running on a 4.7-rc1 tip-based kernel, > the fio test with multithreaded randrw and randwrite tests on the > same file on a XFS partition on top of a NVDIMM with DAX were run, > the aggregated bandwidths before and after the patch were as follows: > > Test BW before patch BW after patch % change > ---- --------------- -------------- -------- > randrw 1210 MB/s 1352 MB/s +12% > randwrite 1622 MB/s 1710 MB/s +5.4% > > The write-only microbench also showed improvement because some read > locking was done by the XFS code. How does a reader only micro-bench react? I'm thinking the extra atomic might hurt a bit.
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[RFC PATCH-tip v2 0/6] locking/rwsem: Enable reader optimistic spinning Waiman Long <Waiman.Long@hpe.com> - 2016-06-15 00:50 +0200
[RFC PATCH-tip v2 2/6] locking/rwsem: Stop active read lock ASAP Waiman Long <Waiman.Long@hpe.com> - 2016-06-15 01:00 +0200
Re: [RFC PATCH-tip v2 2/6] locking/rwsem: Stop active read lock ASAP Peter Zijlstra <peterz@infradead.org> - 2016-06-15 19:30 +0200
Re: [RFC PATCH-tip v2 2/6] locking/rwsem: Stop active read lock ASAP Davidlohr Bueso <dave@stgolabs.net> - 2016-06-16 04:20 +0200
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