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authorYuanhan Liu <yuanhan.liu@linux.intel.com>2013-02-01 18:59:16 +0800
committerIngo Molnar <mingo@kernel.org>2013-02-19 08:43:39 +0100
commit41ef8f826692c8f65882bec0a8211bd4d1d2d19a (patch)
treea59199669e2ffb6f1fffaaee9a98b50fd82d1d96 /kernel/futex.c
parentfe2b05f7ca9f906be61dced5489f63b8b4d7c770 (diff)
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rwsem-spinlock: Implement writer lock-stealing for better scalability
We (Linux Kernel Performance project) found a regression introduced by commit: 5a505085f043 mm/rmap: Convert the struct anon_vma::mutex to an rwsem which converted all anon_vma::mutex locks rwsem write locks. The semantics are the same, but the behavioral difference is quite huge in some cases. After investigating it we found the root cause: mutexes support lock stealing while rwsems don't. Here is the link for the detailed regression report: https://lkml.org/lkml/2013/1/29/84 Ingo suggested adding write lock stealing to rwsems: "I think we should allow lock-steal between rwsem writers - that will not hurt fairness as most rwsem fairness concerns relate to reader vs. writer fairness" And here is the rwsem-spinlock version. With this patch, we got a double performance increase in one test box with following aim7 workfile: FILESIZE: 1M POOLSIZE: 10M 10 fork_test /usr/bin/time output w/o patch /usr/bin/time_output with patch -- Percent of CPU this job got: 369% Percent of CPU this job got: 537% Voluntary context switches: 640595016 Voluntary context switches: 157915561 We got a 45% increase in CPU usage and saved about 3/4 voluntary context switches. Reported-by: LKP project <lkp@linux.intel.com> Suggested-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com> Cc: Alex Shi <alex.shi@intel.com> Cc: David Howells <dhowells@redhat.com> Cc: Michel Lespinasse <walken@google.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Anton Blanchard <anton@samba.org> Cc: Arjan van de Ven <arjan@linux.intel.com> Cc: paul.gortmaker@windriver.com Link: http://lkml.kernel.org/r/1359716356-23865-1-git-send-email-yuanhan.liu@linux.intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
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