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[90.233.221.0]) by smtp.gmail.com with ESMTPSA id 15-20020a2eb94f000000b002d0c1c0e8f0sm172328ljs.33.2024.02.07.05.04.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 07 Feb 2024 05:04:14 -0800 (PST) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Wed, 7 Feb 2024 14:04:12 +0100 To: "Paul E. McKenney" , Andrea Righi Cc: Andrea Righi , Uladzislau Rezki , Joel Fernandes , Joel Fernandes , rcu@vger.kernel.org, "Cc: Frederic Weisbecker" Subject: Re: Observation on NOHZ_FULL Message-ID: References: <6a2b6857-57e7-4321-adae-132ba69a4fff@paulmck-laptop> <0e15e91e-da47-45dd-b7de-7f89b7b6002b@joelfernandes.org> <92cba6df-01de-4daa-a0cb-5fa92c7374dd@paulmck-laptop> 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: <92cba6df-01de-4daa-a0cb-5fa92c7374dd@paulmck-laptop> > > > > I repeated some tests in a more isolated environment and posted the > > results here: > > https://discourse.ubuntu.com/t/enable-low-latency-features-in-the-generic-ubuntu-kernel-for-24-04/42255 > > > > Highlights: > > > > - stress-ng --matrix seems quite unpredictable to be used a benchmarks > > in this scenario (the bogo-ops/s are very susceptible to any kind of > > interference, so even if in the long runs NO_HZ_FULL still seems to > > provide some benefits looking at the average, we also need to > > consider that there might be a significant error in the measurements, > > standard deviation was pretty high) > > > > - fio doing short writes (in page cache) seems to perform like 2x > > better in terms of iops with nohz_full, respect to the other cases > > and it performs 2x slower with large IO writes (not sure why... need > > to investigate more) > > > > - with lazy RCU enabled hrtimer_interrupt() takes like 2x more to > > return, respect to the other cases (is this expected?) > > This last is surprising at first glance, but I could be missing > something. Joel, Uladzislau, thoughts? > Could you please share the steps how you run "fio" tests? -- Uladzislau Rezki