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[141.239.159.203]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-1ef0badcae8sm120624315ad.103.2024.05.15.09.58.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 15 May 2024 09:58:08 -0700 (PDT) Date: Wed, 15 May 2024 06:58:07 -1000 From: Tejun Heo To: Jesper Dangaard Brouer Cc: hannes@cmpxchg.org, lizefan.x@bytedance.com, cgroups@vger.kernel.org, yosryahmed@google.com, longman@redhat.com, netdev@vger.kernel.org, linux-mm@kvack.org, shakeel.butt@linux.dev, kernel-team@cloudflare.com, Arnaldo Carvalho de Melo , Sebastian Andrzej Siewior Subject: Re: [PATCH v1] cgroup/rstat: add cgroup_rstat_cpu_lock helpers and tracepoints Message-ID: References: <171457225108.4159924.12821205549807669839.stgit@firesoul> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <171457225108.4159924.12821205549807669839.stgit@firesoul> X-Rspamd-Queue-Id: 2E034C0018 X-Stat-Signature: dfm67if5i3khgn3wiswg3bjx7zbuyc9e X-Rspam-User: X-Rspamd-Server: rspam11 X-HE-Tag: 1715792297-545787 X-HE-Meta: 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 LdEYbjcz 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.006958, 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, May 01, 2024 at 04:04:11PM +0200, Jesper Dangaard Brouer wrote: > This closely resembles helpers added for the global cgroup_rstat_lock in > commit fc29e04ae1ad ("cgroup/rstat: add cgroup_rstat_lock helpers and > tracepoints"). This is for the per CPU lock cgroup_rstat_cpu_lock. > > Based on production workloads, we observe the fast-path "update" function > cgroup_rstat_updated() is invoked around 3 million times per sec, while the > "flush" function cgroup_rstat_flush_locked(), walking each possible CPU, > can see periodic spikes of 700 invocations/sec. > > For this reason, the tracepoints are split into normal and fastpath > versions for this per-CPU lock. Making it feasible for production to > continuously monitor the non-fastpath tracepoint to detect lock contention > issues. The reason for monitoring is that lock disables IRQs which can > disturb e.g. softirq processing on the local CPUs involved. When the > global cgroup_rstat_lock stops disabling IRQs (e.g converted to a mutex), > this per CPU lock becomes the next bottleneck that can introduce latency > variations. > > A practical bpftrace script for monitoring contention latency: > > bpftrace -e ' > tracepoint:cgroup:cgroup_rstat_cpu_lock_contended { > @start[tid]=nsecs; @cnt[probe]=count()} > tracepoint:cgroup:cgroup_rstat_cpu_locked { > if (args->contended) { > @wait_ns=hist(nsecs-@start[tid]); delete(@start[tid]);} > @cnt[probe]=count()} > interval:s:1 {time("%H:%M:%S "); print(@wait_ns); print(@cnt); clear(@cnt);}' > > Signed-off-by: Jesper Dangaard Brouer Applied to cgroup/for-6.10. Thanks. -- tejun