From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Date: Thu, 22 Oct 2020 15:25:14 +0000 Subject: Re: default cpufreq gov, was: [PATCH] sched/fair: check for idle core Message-Id: <20201022152514.GJ2611@hirez.programming.kicks-ass.net> List-Id: References: <1603211879-1064-1-git-send-email-Julia.Lawall@inria.fr> <34115486.YmRjPRKJaA@kreacher> <20201022120213.GG2611@hirez.programming.kicks-ass.net> <1790766.jaFeG3T87Z@kreacher> <20201022122949.GW2628@hirez.programming.kicks-ass.net> <20201022145250.GK32041@suse.de> In-Reply-To: <20201022145250.GK32041@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Mel Gorman Cc: "Rafael J. Wysocki" , Giovanni Gherdovich , Viresh Kumar , Julia Lawall , Ingo Molnar , kernel-janitors@vger.kernel.org, Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Daniel Bristot de Oliveira , linux-kernel@vger.kernel.org, Valentin Schneider , Gilles Muller , srinivas.pandruvada@linux.intel.com, Linux PM , Len Brown On Thu, Oct 22, 2020 at 03:52:50PM +0100, Mel Gorman wrote: > There are some questions > currently on whether schedutil is good enough when HWP is not available. Srinivas and Rafael will know better, but Intel does run a lot of tests and IIRC it was found that schedutil was on-par for !HWP. That was the basis for commit: 33aa46f252c7 ("cpufreq: intel_pstate: Use passive mode by default without HWP") But now it turns out that commit results in running intel_pstate-passive on ondemand, which is quite horrible. > There was some evidence (I don't have the data, Giovanni was looking into > it) that HWP was a requirement to make schedutil work well. That seems to be the question; Rafael just said the opposite. > For distros, switching to schedutil by default would be nice because > frequency selection state would follow the task instead of being per-cpu > and we could stop worrying about different HWP implementations but it's s/HWP/cpufreq-governors/ ? But yes. > not at the point where the switch is advisable. I would expect hard data > before switching the default and still would strongly advise having a > period of time where we can fall back when someone inevitably finds a > new corner case or exception. Which is why I advocated to make it 'difficult' to use the old ones and only later remove them. > For reference, SLUB had the same problem for years. It was switched > on by default in the kernel config but it was a long time before > SLUB was generally equivalent to SLAB in terms of performance. I remember :-)