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[209.85.218.51]) by smtp.gmail.com with ESMTPSA id h19sm5494096ejb.66.2020.05.21.11.38.47 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 21 May 2020 11:38:47 -0700 (PDT) Received: by mail-ej1-f51.google.com with SMTP id x1so10040746ejd.8 for ; Thu, 21 May 2020 11:38:47 -0700 (PDT) X-Received: by 2002:a2e:7e0a:: with SMTP id z10mr3496127ljc.314.1590085914996; Thu, 21 May 2020 11:31:54 -0700 (PDT) MIME-Version: 1.0 References: <20200520222642.70679-1-joel@joelfernandes.org> In-Reply-To: <20200520222642.70679-1-joel@joelfernandes.org> From: Linus Torvalds Date: Thu, 21 May 2020 11:31:38 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH RFC] sched: Add a per-thread core scheduling interface To: "Joel Fernandes (Google)" Cc: Nishanth Aravamudan , Julien Desfossez , Peter Zijlstra , Tim Chen , Ingo Molnar , Thomas Gleixner , Paul Turner , vpillai , Linux Kernel Mailing List , =?UTF-8?B?RnLDqWTDqXJpYyBXZWlzYmVja2Vy?= , Kees Cook , Greg Kerr , Phil Auld , Aaron Lu , Aubrey Li , aubrey.li@linux.intel.com, Valentin Schneider , Mel Gorman , Pawan Gupta , Paolo Bonzini , Joel Fernandes Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 20, 2020 at 3:26 PM Joel Fernandes (Google) wrote: > > ChromeOS will use core-scheduling to securely enable hyperthreading. > This cuts down the keypress latency in Google docs from 150ms to 50ms > while improving the camera streaming frame rate by ~3%. I'm assuming this is "compared to SMT disabled"? What is the cost compared to "SMT enabled but no core scheduling"? But the real reason I'm piping up is that your latency benchmark sounds very cool. Generally throughput benchmarks are much easier to do, how do you do this latency benchmark, and is it perhaps something that could be run more widely (ie I'm thinking that if it's generic enough and stable enough to be run by some of the performance regression checking robots, it would be a much more interesting test-case than some of the ones they run right now...) I'm looking at that "threaded phoronix gzip performance regression" thread due to a totally unrelated scheduling change ("sched/fair: Rework load_balance()"), and then I see this thread and my reaction is "the keypress latency thing sounds like a much more interesting performance test than threaded gzip from clear linux". But the threaded gzip test is presumably trivial to script, while your latency test is perhaps very specific to one particular platform and setuip? Linus