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[173.180.45.4]) by smtp.gmail.com with ESMTPSA id on17sm3203862pjb.40.2022.02.24.08.29.23 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Thu, 24 Feb 2022 08:29:24 -0800 (PST) From: "Doug Smythies" To: Cc: "'Rafael J. Wysocki'" , "'srinivas pandruvada'" , "'Zhang, Rui'" , "'Thomas Gleixner'" , , , , "Doug Smythies" , "'Feng Tang'" References: <20220222073435.GB78951@shbuild999.sh.intel.com> <24f7d485dc60ba3ed5938230f477bf22a220d596.camel@linux.intel.com> <20220223004041.GA4548@shbuild999.sh.intel.com> <20220224080830.GD4548@shbuild999.sh.intel.com> <20220224144423.GV4285@paulmck-ThinkPad-P17-Gen-1> In-Reply-To: <20220224144423.GV4285@paulmck-ThinkPad-P17-Gen-1> Subject: RE: CPU excessively long times between frequency scaling driver calls - bisected Date: Thu, 24 Feb 2022 08:29:22 -0800 Message-ID: <002901d8299b$af50d6d0$0df28470$@telus.net> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit X-Mailer: Microsoft Outlook 16.0 Content-Language: en-ca Thread-Index: AQJoYM4LcAz85xHF3s1ly2J0+vMjpQK6V02BAMrH5oYB+Ch6FQG4OsPxAq/kLv0CiDg/5AHRugzUAltSUdoBsNWicwNgeW4nqtUP4XA= Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On 2022.02.24 04:08:30 Paul E. McKenney wrote: > On Thu, Feb 24, 2022 at 04:08:30PM +0800, Feng Tang wrote: >> On Wed, Feb 23, 2022 at 03:23:20PM +0100, Rafael J. Wysocki wrote: >>> On Wed, Feb 23, 2022 at 1:40 AM Feng Tang wrote: >>> >>> But this is not related to idle as such, but to the fact that idle >>> sometimes stops the scheduler tick which otherwise would run the >>> cpufreq governor callback on a regular basis. >>> >>> It is stopping the tick that gets us into trouble, so I would avoid >>> doing it if the current performance state is too aggressive. >> >> I've tried to simulate Doug's environment by using his kconfig, and >> offline my 36 CPUs Desktop to leave 12 CPUs online, and on it I can >> still see Local timer interrupts when there is no active load, with >> the longest interval between 2 timer interrupts is 4 seconds, while >> idle class's task_tick_idle() will do nothing, and CFS' >> task_tick_fair() will in turn call cfs_rq_util_change() > > Every four seconds? Could you please post your .config? > > Thanx, Paul I steal the kernel config from the Ubuntu mainline PPA. See also earlier on this thread: https://lore.kernel.org/linux-pm/CAAYoRsXkyWf0vmEE2HvjF6pzCC4utxTF=7AFx1PJv4Evh=C+Ow@mail.gmail.com/ but relevant part copied here: > I steal the kernel configuration file from the Ubuntu mainline PPA > [1], what they call "lowlatency", or 1000Hz tick. I make these > changes before compile: > > scripts/config --disable DEBUG_INFO > scripts/config --disable SYSTEM_TRUSTED_KEYS > scripts/config --disable SYSTEM_REVOCATION_KEYS > > I [will] also send you the config and dmesg files in an off-list email. > > [1] https://kernel.ubuntu.com/~kernel-ppa/mainline/v5.17-rc3/ I put the same one I sent Feng on my web site where I was sharing stuff with Srinivas (coded to avoid the barrage of bots): double u double u double u dot smythies dot com/~doug/linux/s18/hwp/srinivas/long_dur/ ... Doug