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b=lp7id31/DO3cqmmJWSYyKj3SbbCKrsQYjRLojLlcyZTXYrnJG8976Nn09wkdlJq5+ vntIt9AWHByAEawJYfwSpqbw1uuJaqynLnglzNZLHlHACQMEDIeex8ONioxwRtaYj5 s2edM2YNVUfhYZukoxULhJXayB6nxxxwSo/DxSm2bQc22PLhd+3oDIY3BoXA78tWAN BZ5FXkn/xvqnXUA1TEVGZO2tMT1l2QDfkzgo+htilP/eHf05dkTEG4fHr/zjM6V5Sa jFIcc7QV0SazaJyK9/aU0tfxdA0rHrHfHbGdKCdI18PQiqWjE71Hf9wHJKVCPTwFF/ XLY7Vy8MwF4Vw== Date: Wed, 19 Mar 2025 07:26:04 -1000 From: Tejun Heo To: Greg Thelen Cc: Johannes Weiner , Michal =?iso-8859-1?Q?Koutn=FD?= , Andrew Morton , Eric Dumazet , Yosry Ahmed , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Eric Dumazet Subject: Re: [PATCH] cgroup/rstat: avoid disabling irqs for O(num_cpu) Message-ID: References: <20250319071330.898763-1-gthelen@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250319071330.898763-1-gthelen@google.com> X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 4D78F2001C X-Stat-Signature: d6p9kzw87n1i5tgz87gqf4mckde1hb76 X-HE-Tag: 1742405167-272827 X-HE-Meta: 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 2sw13+cK 5qF+EDq+eSpQT06omVVadArneU4nEJsWP4thnAMiuGVu3kjl3lzyQgOrHjpYD5JkWI4zetDibgNbvKRLmJJKbJ4E8uPcgDz0UJpTSNSpR2/CRXXfICvhN+3X4LcfRYg8w3Eh0hbIxEj0DKbUtS7O76S+HkBiq3KgM7oOf0MNuNOTgto0Art6OU5KL3C99ch7ZU29A7o6u4OBa1W6B7mBM2BoMG9WZHSQ5Id5ovmBcloNwmLisEGKIpoCLq7aL7i6hUBlHOR3NKtoQpq/ljoSS+78pFzjgDenwS+1tedzvyN5JKgeNrBifmlddLXTKzPgGuM0Upq5q3Gc8roFWQfaiX6b8hw2wQZWkFAKytWllgM+q7Q4Tm0TBAknZdw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Mar 19, 2025 at 12:13:30AM -0700, Greg Thelen wrote: > From: Eric Dumazet > > cgroup_rstat_flush_locked() grabs the irq safe cgroup_rstat_lock while > iterating all possible cpus. It only drops the lock if there is > scheduler or spin lock contention. If neither, then interrupts can be > disabled for a long time. On large machines this can disable interrupts > for a long enough time to drop network packets. On 400+ CPU machines > I've seen interrupt disabled for over 40 msec. > > Prevent rstat from disabling interrupts while processing all possible > cpus. Instead drop and reacquire cgroup_rstat_lock for each cpu. This > approach was previously discussed in > https://lore.kernel.org/lkml/ZBz%2FV5a7%2F6PZeM7S@slm.duckdns.org/, > though this was in the context of an non-irq rstat spin lock. > > Benchmark this change with: > 1) a single stat_reader process with 400 threads, each reading a test > memcg's memory.stat repeatedly for 10 seconds. > 2) 400 memory hog processes running in the test memcg and repeatedly > charging memory until oom killed. Then they repeat charging and oom > killing. > > v6.14-rc6 with CONFIG_IRQSOFF_TRACER with stat_reader and hogs, finds > interrupts are disabled by rstat for 45341 usec: > # => started at: _raw_spin_lock_irq > # => ended at: cgroup_rstat_flush > # > # > # _------=> CPU# > # / _-----=> irqs-off/BH-disabled > # | / _----=> need-resched > # || / _---=> hardirq/softirq > # ||| / _--=> preempt-depth > # |||| / _-=> migrate-disable > # ||||| / delay > # cmd pid |||||| time | caller > # \ / |||||| \ | / > stat_rea-96532 52d.... 0us*: _raw_spin_lock_irq > stat_rea-96532 52d.... 45342us : cgroup_rstat_flush > stat_rea-96532 52d.... 45342us : tracer_hardirqs_on <-cgroup_rstat_flush > stat_rea-96532 52d.... 45343us : > => memcg1_stat_format > => memory_stat_format > => memory_stat_show > => seq_read_iter > => vfs_read > => ksys_read > => do_syscall_64 > => entry_SYSCALL_64_after_hwframe > > With this patch the CONFIG_IRQSOFF_TRACER doesn't find rstat to be the > longest holder. The longest irqs-off holder has irqs disabled for > 4142 usec, a huge reduction from previous 45341 usec rstat finding. > > Running stat_reader memory.stat reader for 10 seconds: > - without memory hogs: 9.84M accesses => 12.7M accesses > - with memory hogs: 9.46M accesses => 11.1M accesses > The throughput of memory.stat access improves. > > The mode of memory.stat access latency after grouping by of 2 buckets: > - without memory hogs: 64 usec => 16 usec > - with memory hogs: 64 usec => 8 usec > The memory.stat latency improves. > > Signed-off-by: Eric Dumazet > Signed-off-by: Greg Thelen > Tested-by: Greg Thelen Applied to cgroup/for-6.15. Thanks. -- tejun