From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave Chinner Subject: Re: [PATCH 00/46] rcu-walk and dcache scaling Date: Wed, 8 Dec 2010 15:28:16 +1100 Message-ID: <20101208042816.GA32766@dastard> References: <20101207215653.GA25864@dastard> <20101208033212.GF29333@dastard> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Nick Piggin , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org To: Nick Piggin Return-path: Content-Disposition: inline In-Reply-To: <20101208033212.GF29333@dastard> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Wed, Dec 08, 2010 at 02:32:12PM +1100, Dave Chinner wrote: > On Wed, Dec 08, 2010 at 12:47:42PM +1100, Nick Piggin wrote: > > On Wed, Dec 8, 2010 at 8:56 AM, Dave Chinner = wrote: > > > On Sat, Nov 27, 2010 at 09:15:58PM +1100, Nick Piggin wrote: > > >> > > >> git://git.kernel.org/pub/scm/linux/kernel/git/npiggin/linux-npig= gin.git vfs-scale-working > > >> > > >> Here is an new set of vfs patches for review, not that there was= much interest > > >> last time they were posted. It is structured like: > > >> > > >> * preparation patches > > >> * introduce new locks to take over dcache_lock, then remove it > > >> * cleaning up and reworking things for new locks > > >> * rcu-walk path walking > > >> * start on some fine grained locking steps > > > > > > Stress test doing: > > > > > > =A0 =A0 =A0 =A0single thread 50M inode create > > > =A0 =A0 =A0 =A0single thread rm -rf > > > =A0 =A0 =A0 =A02-way 50M inode create > > > =A0 =A0 =A0 =A02-way rm -rf > > > =A0 =A0 =A0 =A04-way 50M inode create > > > =A0 =A0 =A0 =A04-way rm -rf > > > =A0 =A0 =A0 =A08-way 50M inode create > > > =A0 =A0 =A0 =A08-way rm -rf > > > =A0 =A0 =A0 =A08-way 250M inode create > > > =A0 =A0 =A0 =A08-way rm -rf > > > > > > Failed about 5 minutes into the "4-way rm -rf" (~3 hours into the= test) > > > with a CPU stuck spinning on here: > > > > > > [37372.084012] NMI backtrace for cpu 5 > > > [37372.084012] CPU 5 > > > [37372.084012] Modules linked in: > > > [37372.084012] > > > [37372.084012] Pid: 15214, comm: rm Not tainted 2.6.37-rc4-dgc+ #= 797 /Bochs > > > [37372.084012] RIP: 0010:[] =A0[] __ticket_spin_lock+0x14/0x20 > > > [37372.084012] RSP: 0018:ffff880114643c98 =A0EFLAGS: 00000213 > > > [37372.084012] RAX: 0000000000008801 RBX: ffff8800687be6c0 RCX: f= fff8800c4eb2688 > > > [37372.084012] RDX: ffff880114643d38 RSI: ffff8800dfd4ea80 RDI: f= fff880114643d14 > > > [37372.084012] RBP: ffff880114643c98 R08: 0000000000000003 R09: 0= 000000000000000 > > > [37372.084012] R10: 0000000000000000 R11: dead000000200200 R12: f= fff880114643d14 > > > [37372.084012] R13: ffff880114643cb8 R14: ffff880114643d38 R15: f= fff8800687be71c > > > [37372.084012] FS: =A000007fd6d7c93700(0000) GS:ffff8800dfd40000(= 0000) knlGS:0000000000000000 > > > [37372.084012] CS: =A00010 DS: 0000 ES: 0000 CR0: 000000008005003= b > > > [37372.084012] CR2: 0000000000bbd108 CR3: 0000000107146000 CR4: 0= 0000000000006e0 > > > [37372.084012] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0= 000000000000000 > > > [37372.084012] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0= 000000000000400 > > > [37372.084012] Process rm (pid: 15214, threadinfo ffff88011464200= 0, task ffff88011b16f890) > > > [37372.084012] Stack: > > > [37372.084012] =A0ffff880114643ca8 ffffffff81ad044e ffff880114643= cf8 ffffffff81167ae7 > > > [37372.084012] =A00000000000000000 ffff880114643d38 0000000000000= 00e ffff88011901d800 > > > [37372.084012] =A0ffff8800cdb7cf5c ffff88011901d8e0 0000000000000= 000 0000000000000000 > > > [37372.084012] Call Trace: > > > [37372.084012] =A0[] _raw_spin_lock+0xe/0x20 > > > [37372.084012] =A0[] shrink_dentry_list+0x47/0x= 370 > > > [37372.084012] =A0[] __shrink_dcache_sb+0x14e/0= x1e0 > > > [37372.084012] =A0[] shrink_dcache_parent+0x276= /0x2d0 > > > [37372.084012] =A0[] ? _raw_spin_lock+0xe/0x20 > > > [37372.084012] =A0[] dentry_unhash+0x42/0x80 > > > [37372.084012] =A0[] vfs_rmdir+0x68/0x100 > > > [37372.084012] =A0[] do_rmdir+0x113/0x130 > > > [37372.084012] =A0[] ? filp_close+0x5d/0x90 > > > [37372.084012] =A0[] sys_unlinkat+0x35/0x40 > > > [37372.084012] =A0[] system_call_fastpath+0x16/= 0x1b > >=20 > > OK good, with any luck, that's the same bug. > >=20 > > Is this XFS? >=20 > Yes. >=20 > > Is there any concurrent activity happening on the same dentries? >=20 > Not from an application perspective. >=20 > > Ie. are the rm -rf threads running on the same directories, >=20 > No, each thread operating on a different directory. >=20 > > or is there any reclaim happening in the background? >=20 > IIRC, kswapd was consuming about 5-10% of a CPU during parallel > unlink tests. Mainly reclaiming XFS inodes, I think, but there may > be dentry cache reclaim going as well. Turns out that the kswapd peaks are upwards of 50% of a CPU for a few seconds, then idle for 10-15s. Typical perf top output of kswapd while it is active during unlinks is: samples pcnt function DSO _______ _____ ___________________________ ________________= _ 17168.00 10.2% __call_rcu [kernel.kallsyms= ] 13223.00 7.8% kmem_cache_free [kernel.kallsyms= ] 12917.00 7.6% down_write [kernel.kallsyms= ] 12665.00 7.5% xfs_iunlock [kernel.kallsyms= ] 10493.00 6.2% xfs_reclaim_inode_grab [kernel.kallsyms= ] 9314.00 5.5% __lookup_tag [kernel.kallsyms= ] 9040.00 5.4% radix_tree_delete [kernel.kallsyms= ] 8694.00 5.1% is_bad_inode [kernel.kallsyms= ] 7639.00 4.5% __ticket_spin_lock [kernel.kallsyms= ] 6821.00 4.0% _raw_spin_unlock_irqrestore [kernel.kallsyms= ] 5484.00 3.2% __d_drop [kernel.kallsyms= ] 5114.00 3.0% xfs_reclaim_inode [kernel.kallsyms= ] 4626.00 2.7% __rcu_process_callbacks [kernel.kallsyms= ] 3556.00 2.1% up_write [kernel.kallsyms= ] 3206.00 1.9% _cond_resched [kernel.kallsyms= ] 3129.00 1.9% xfs_qm_dqdetach [kernel.kallsyms= ] 2327.00 1.4% radix_tree_tag_clear [kernel.kallsyms= ] 2327.00 1.4% call_rcu_sched [kernel.kallsyms= ] 2262.00 1.3% __ticket_spin_unlock [kernel.kallsyms= ] 2215.00 1.3% xfs_ilock [kernel.kallsyms= ] 2200.00 1.3% radix_tree_gang_lookup_tag [kernel.kallsyms= ] 1982.00 1.2% xfs_reclaim_inodes_ag [kernel.kallsyms= ] 1736.00 1.0% xfs_trans_unlocked_item [kernel.kallsyms= ] 1707.00 1.0% __ticket_spin_trylock [kernel.kallsyms= ] 1688.00 1.0% xfs_perag_get_tag [kernel.kallsyms= ] 1660.00 1.0% flat_send_IPI_mask [kernel.kallsyms= ] 1538.00 0.9% xfs_inode_item_destroy [kernel.kallsyms= ] 1312.00 0.8% __shrink_dcache_sb [kernel.kallsyms= ] 940.00 0.6% xfs_perag_put [kernel.kallsyms= ] So there is some dentry cache reclaim going on.=20 =46WIW, it appears there is quite a lot of RCU freeing overhead (~15% more CPU time) in the work kswapd is doing during these unlinks, too. I just had a look at kswapd when a 8-way create is running - it's runni= ng at 50-60% of a cpu for seconds at a time. I caught this while it was doing= pure XFS inode cache reclaim (~10s sample, kswapd reclaimed ~1M inodes): samples pcnt function DSO _______ _____ ___________________________ ________________= _ 27171.00 9.0% __call_rcu [kernel.kallsyms= ] 21491.00 7.1% down_write [kernel.kallsyms= ] 20916.00 6.9% xfs_reclaim_inode [kernel.kallsyms= ] 20313.00 6.7% radix_tree_delete [kernel.kallsyms= ] 15828.00 5.3% kmem_cache_free [kernel.kallsyms= ] 15819.00 5.2% xfs_idestroy_fork [kernel.kallsyms= ] 14893.00 4.9% is_bad_inode [kernel.kallsyms= ] 14666.00 4.9% _raw_spin_unlock_irqrestore [kernel.kallsyms= ] 14191.00 4.7% xfs_reclaim_inode_grab [kernel.kallsyms= ] 14105.00 4.7% xfs_iunlock [kernel.kallsyms= ] 10916.00 3.6% __ticket_spin_lock [kernel.kallsyms= ] 10125.00 3.4% xfs_iflush_cluster [kernel.kallsyms= ] 8221.00 2.7% xfs_qm_dqdetach [kernel.kallsyms= ] 7639.00 2.5% xfs_trans_unlocked_item [kernel.kallsyms= ] 7028.00 2.3% xfs_synchronize_times [kernel.kallsyms= ] 6974.00 2.3% up_write [kernel.kallsyms= ] 5870.00 1.9% call_rcu_sched [kernel.kallsyms= ] 5634.00 1.9% _cond_resched [kernel.kallsyms= ] Which is showing a similar amount of RCU overhead as the unlink as abov= e. And this while it was doing dentry cache reclaim (~10s sample): 35921.00 15.7% __d_drop [kernel.kallsy= ms] 30056.00 13.1% __ticket_spin_trylock [kernel.kallsy= ms] 29066.00 12.7% __ticket_spin_lock [kernel.kallsy= ms] 19043.00 8.3% __call_rcu [kernel.kallsy= ms] 10098.00 4.4% iput [kernel.kallsy= ms] 7013.00 3.1% __shrink_dcache_sb [kernel.kallsy= ms] 6774.00 3.0% __percpu_counter_add [kernel.kallsy= ms] 6708.00 2.9% radix_tree_tag_set [kernel.kallsy= ms] 5362.00 2.3% xfs_inactive [kernel.kallsy= ms] 5130.00 2.2% __ticket_spin_unlock [kernel.kallsy= ms] 4884.00 2.1% call_rcu_sched [kernel.kallsy= ms] 4621.00 2.0% dentry_lru_del [kernel.kallsy= ms] 3735.00 1.6% bit_waitqueue [kernel.kallsy= ms] 3727.00 1.6% dentry_iput [kernel.kallsy= ms] 3473.00 1.5% shrink_icache_memory [kernel.kallsy= ms] 3279.00 1.4% kfree [kernel.kallsy= ms] 3101.00 1.4% xfs_perag_get [kernel.kallsy= ms] 2516.00 1.1% kmem_cache_free [kernel.kallsy= ms] 2272.00 1.0% shrink_dentry_list [kernel.kallsy= ms] I've never really seen any signficant dentry cache reclaim overhead in profiles of these workloads before, so this was a bit of a surprise.... Cheers, Dave. --=20 Dave Chinner david@fromorbit.com