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[90.235.18.79]) by smtp.gmail.com with ESMTPSA id j17-20020ac253b1000000b00511696f0d95sm804768lfh.203.2024.02.12.01.44.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 12 Feb 2024 01:44:27 -0800 (PST) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Mon, 12 Feb 2024 10:44:25 +0100 To: Joel Fernandes Cc: Uladzislau Rezki , Andrea Righi , "Paul E. McKenney" , Joel Fernandes , rcu@vger.kernel.org, "Cc: Frederic Weisbecker" Subject: Re: Observation on NOHZ_FULL Message-ID: References: <9f9b6885-6d9d-4f30-9635-49443e1615e9@joelfernandes.org> <1fcf7e8a-c245-4c5c-ac86-7f0a1531032d@joelfernandes.org> <29e6c22d-0487-42a5-b840-e3c7ea7c6270@joelfernandes.org> Precedence: bulk X-Mailing-List: rcu@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <29e6c22d-0487-42a5-b840-e3c7ea7c6270@joelfernandes.org> > >> > >> I have done some basic research about hrtimer_interrupt() latency on my > >> HW with latest Linux kernel. I have compared below cases: > >> > >> case a: 1000HZ + lazy + nocb_all_cpus > >> case b: 1000HZ + nocb_all_cpus > >> > >> I used "ftrace" to measure time(in microseconds). Steps: > >> > >> echo 0 > tracing_on > >> echo function_graph > current_tracer > >> echo funcgraph-proc > trace_options > >> echo funcgraph-abstime > trace_options > >> echo hrtimer_interrupt > set_ftrace_filter > >> > >> fio --rw=write --bs=1M --size=1G --numjobs=8 --name=worker --time_based --runtime=50& > >> > >> echo 1 > tracing_on; sleep 10; echo 0 > tracing_on > >> > >> data is based on 10 seconds collection: > >> > >> > >> 6 2102 ############################################################ > >> 8 2079 ############################################################ > >> 10 1464 ########################################## > >> 7 897 ########################## > > So first column is microseconds and second one is count? > Right! > >> 9 625 ################## > >> 12 490 ############## > >> 13 479 ############## > >> 11 289 ######### > >> 5 249 ######## > >> 14 124 #### > >> 15 72 ### > >> 16 41 ## > >> 17 24 # > >> 4 22 # > >> 18 12 # > >> 22 2 # > >> 19 1 # > >> > >> > >> > >> 9 1658 ############################################################ > >> 13 1308 ################################################ > >> 12 1224 ############################################# > > Assuming that, it does seem the "best" case is off by 3 microseconds (9 vs 6), > still would not warrant being regarded a bug and possibly just in the noise. > I also think it is a noise.