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Date: Tue, 14 Jun 2011 17:29:58 -0700 From: Tim Chen <tim.c.chen@...ux.intel.com> To: Peter Zijlstra <a.p.zijlstra@...llo.nl>, Andrew Morton <akpm@...ux-foundation.org>, Linus Torvalds <torvalds@...ux-foundation.org> Cc: Hugh Dickins <hughd@...gle.com>, KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>, Benjamin Herrenschmidt <benh@...nel.crashing.org>, David Miller <davem@...emloft.net>, Martin Schwidefsky <schwidefsky@...ibm.com>, Russell King <rmk@....linux.org.uk>, Paul Mundt <lethal@...ux-sh.org>, Jeff Dike <jdike@...toit.com>, Richard Weinberger <richard@....at>, Tony Luck <tony.luck@...el.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>, Mel Gorman <mel@....ul.ie>, Nick Piggin <npiggin@...nel.dk>, Namhyung Kim <namhyung@...il.com>, ak@...ux.intel.com, shaohua.li@...el.com, alex.shi@...el.com, linux-kernel@...r.kernel.org, linux-mm@...ck.org, "Rafael J. Wysocki" <rjw@...k.pl> Subject: REGRESSION: Performance regressions from switching anon_vma->lock to mutex It seems like that the recent changes to make the anon_vma->lock into a mutex (commit 2b575eb6) causes a 52% regression in throughput (2.6.39 vs 3.0-rc2) on exim mail server workload in the MOSBENCH test suite. Our test setup is on a 4 socket Westmere EX system, with 10 cores per socket. 40 clients are created on the test machine which send email to the exim server residing on the sam test machine. Exim forks off child processes to handle the incoming mail, and the process exits after the mail delivery completes. We see quite a bit of acquisition of the anon_vma->lock as a result. On 2.6.39, the contention of anon_vma->lock occupies 3.25% of cpu. However, after the switch of the lock to mutex on 3.0-rc2, the mutex acquisition jumps to 18.6% of cpu. This seems to be the main cause of the 52% throughput regression. Other workloads which have a lot of forks/exits may be similarly affected by this regression. Workloads which are vm lock intensive could be affected too. I've listed the profile of 3.0-rc2 and 2.6.39 below for comparison. Thanks. Tim --------------------------- 3.0-rc2 profile: - 18.60% exim [kernel.kallsyms] [k] __mutex_lock_common.clone.5 - __mutex_lock_common.clone.5 - 99.99% __mutex_lock_slowpath - mutex_lock - 99.54% anon_vma_lock.clone.10 + 38.99% anon_vma_clone + 37.56% unlink_anon_vmas + 11.92% anon_vma_fork + 11.53% anon_vma_free + 4.03% exim [kernel.kallsyms] [k] _raw_spin_lock_irqsave - 3.00% exim [kernel.kallsyms] [k] do_raw_spin_lock - do_raw_spin_lock - 94.11% _raw_spin_lock + 47.32% __mutex_lock_common.clone.5 + 14.23% __mutex_unlock_slowpath + 4.06% handle_pte_fault + 3.81% __do_fault + 3.16% unmap_vmas + 2.46% lock_flocks + 2.43% copy_pte_range + 2.28% __task_rq_lock + 1.30% __percpu_counter_add + 1.30% dput + 1.27% add_partial + 1.24% free_pcppages_bulk + 1.07% d_alloc + 1.07% get_page_from_freelist + 1.02% complete_walk + 0.89% dget + 0.71% new_inode + 0.61% __mod_timer + 0.58% dup_fd + 0.50% double_rq_lock + 3.66% _raw_spin_lock_irq + 0.87% _raw_spin_lock_bh + 2.90% exim [kernel.kallsyms] [k] page_fault + 2.25% exim [kernel.kallsyms] [k] mutex_unlock ----------------------------------- 2.6.39 profile: + 4.84% exim [kernel.kallsyms] [k] page_fault + 3.83% exim [kernel.kallsyms] [k] clear_page_c - 3.25% exim [kernel.kallsyms] [k] do_raw_spin_lock - do_raw_spin_lock - 91.86% _raw_spin_lock + 14.16% unlink_anon_vmas + 12.54% unlink_file_vma + 7.30% anon_vma_clone_batch + 6.17% dup_mm + 5.77% __do_fault + 5.77% __pte_alloc + 5.31% lock_flocks ... + 3.22% exim [kernel.kallsyms] [k] unmap_vmas + 2.27% exim [kernel.kallsyms] [k] page_cache_get_speculative + 2.02% exim [kernel.kallsyms] [k] copy_page_c + 1.63% exim [kernel.kallsyms] [k] __list_del_entry + 1.58% exim [kernel.kallsyms] [k] get_page_from_freelist -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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