Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755570AbXJCJdc (ORCPT ); Wed, 3 Oct 2007 05:33:32 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752656AbXJCJdY (ORCPT ); Wed, 3 Oct 2007 05:33:24 -0400 Received: from pentafluge.infradead.org ([213.146.154.40]:43966 "EHLO pentafluge.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751777AbXJCJdX (ORCPT ); Wed, 3 Oct 2007 05:33:23 -0400 Subject: [PATCH] lockstat: documentation From: Peter Zijlstra To: Randy Dunlap Cc: Andrew Morton , lkml , Zach Brown , Ingo Molnar In-Reply-To: <20071002084239.7371820c.randy.dunlap@oracle.com> References: <92cbf19b0709272332s25684643odaade0e98cb3a1f4@mail.gmail.com> <20070927235034.ae7bd73d.akpm@linux-foundation.org> <1190998853.6702.17.camel@heimdal.trondhjem.org> <20070928114930.2c201324.akpm@linux-foundation.org> <1191005339.18147.89.camel@lappy> <20070928121642.56a380ce.akpm@linux-foundation.org> <1191332161.13204.70.camel@twins> <20071002084239.7371820c.randy.dunlap@oracle.com> Content-Type: text/plain Date: Wed, 03 Oct 2007 11:28:08 +0200 Message-Id: <1191403688.5572.3.camel@lappy> Mime-Version: 1.0 X-Mailer: Evolution 2.12.0 Content-Transfer-Encoding: 7bit X-Bad-Reply: References and In-Reply-To but no 'Re:' in Subject. Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7945 Lines: 160 Thanks Randy! update patch below. --- Subject: lockstat: documentation Provide some documentation for CONFIG_LOCK_STAT Signed-off-by: Peter Zijlstra --- Documentation/lockstat.txt | 120 +++++++++++++++++++++++++++++++++++++++++++++ lib/Kconfig.debug | 2 2 files changed, 122 insertions(+) Index: linux-2.6/Documentation/lockstat.txt =================================================================== --- /dev/null +++ linux-2.6/Documentation/lockstat.txt @@ -0,0 +1,120 @@ + +LOCK STATISTICS + +- WHAT + +As the name suggests, it provides statistics on locks. + +- WHY + +Because things like lock contention can severely impact performance. + +- HOW + +Lockdep already has hooks in the lock functions and maps lock instances to +lock classes. We build on that. The graph below shows the relation between +the lock functions and the various hooks therein. + + __acquire + | + lock _____ + | \ + | __contended + | | + | + | _______/ + |/ + | + __acquired + | + . + + . + | + __release + | + unlock + +lock, unlock - the regular lock functions +__* - the hooks +<> - states + +With these hooks we provide the following statistics: + + con-bounces - number of lock contention that involved x-cpu data + contentions - number of lock acquisitions that had to wait + wait time min - shortest (non-0) time we ever had to wait for a lock + max - longest time we ever had to wait for a lock + total - total time we spend waiting on this lock + acq-bounces - number of lock acquisitions that involved x-cpu data + acquisitions - number of times we took the lock + hold time min - shortest (non-0) time we ever held the lock + max - longest time we ever held the lock + total - total time this lock was held + +From these number various other statistics can be derived, such as: + + hold time average = hold time total / acquisitions + +These numbers are gathered per lock class, per read/write state (when +applicable). + +It also tracks 4 contention points per class. A contention point is a call site +that had to wait on lock acquisition. + + - USAGE + +Look at the current lock statistics: + +( line numbers not part of actual output, done for clarity in the explanation + below ) + +# less /proc/lock_stat + +01 lock_stat version 0.2 +02 ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- +03 class name con-bounces contentions waittime-min waittime-max waittime-total acq-bounces acquisitions holdtime-min holdtime-max holdtime-total +04 ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- +05 +06 &inode->i_data.tree_lock-W: 15 21657 0.18 1093295.30 11547131054.85 58 10415 0.16 87.51 6387.60 +07 &inode->i_data.tree_lock-R: 0 0 0.00 0.00 0.00 23302 231198 0.25 8.45 98023.38 +08 -------------------------- +09 &inode->i_data.tree_lock 0 [] add_to_page_cache+0x5f/0x190 +10 +11 ............................................................................................................................................................................................... +12 +13 dcache_lock: 1037 1161 0.38 45.32 774.51 6611 243371 0.15 306.48 77387.24 +14 ----------- +15 dcache_lock 180 [] sys_getcwd+0x11e/0x230 +16 dcache_lock 165 [] d_alloc+0x15a/0x210 +17 dcache_lock 33 [] _atomic_dec_and_lock+0x4d/0x70 +18 dcache_lock 1 [] shrink_dcache_parent+0x18/0x130 + +This excerpt shows the first two lock class statistics. Line 01 shows the +output version - each time the format changes this will be updated. Line 02-04 +show the header with column descriptions. Lines 05-10 and 13-18 show the actual +statistics. These statistics come in two parts; the actual stats separated by a +short separator (line 08, 14) from the contention points. + +The first lock (05-10) is a read/write lock, and shows two lines above the +short separator. The contention points don't match the column descriptors, +they have two: contentions and [] symbol. + + +View the top contending locks: + +# grep : /proc/lock_stat | head + &inode->i_data.tree_lock-W: 15 21657 0.18 1093295.30 11547131054.85 58 10415 0.16 87.51 6387.60 + &inode->i_data.tree_lock-R: 0 0 0.00 0.00 0.00 23302 231198 0.25 8.45 98023.38 + dcache_lock: 1037 1161 0.38 45.32 774.51 6611 243371 0.15 306.48 77387.24 + &inode->i_mutex: 161 286 18446744073709 62882.54 1244614.55 3653 20598 18446744073709 62318.60 1693822.74 + &zone->lru_lock: 94 94 0.53 7.33 92.10 4366 32690 0.29 59.81 16350.06 + &inode->i_data.i_mmap_lock: 79 79 0.40 3.77 53.03 11779 87755 0.28 116.93 29898.44 + &q->__queue_lock: 48 50 0.52 31.62 86.31 774 13131 0.17 113.08 12277.52 + &rq->rq_lock_key: 43 47 0.74 68.50 170.63 3706 33929 0.22 107.99 17460.62 + &rq->rq_lock_key#2: 39 46 0.75 6.68 49.03 2979 32292 0.17 125.17 17137.63 + tasklist_lock-W: 15 15 1.45 10.87 32.70 1201 7390 0.58 62.55 13648.47 + +Clear the statistics: + +# echo 0 > /proc/lock_stat Index: linux-2.6/lib/Kconfig.debug =================================================================== --- linux-2.6.orig/lib/Kconfig.debug +++ linux-2.6/lib/Kconfig.debug @@ -309,6 +309,8 @@ config LOCK_STAT help This feature enables tracking lock contention points + For more details, see Documentation/lockstat.txt + config DEBUG_LOCKDEP bool "Lock dependency engine debugging" depends on DEBUG_KERNEL && LOCKDEP - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/