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imf14.hostedemail.com; dkim=none; dmarc=none; spf=pass (imf14.hostedemail.com: domain of hdanton@sina.com designates 202.108.3.17 as permitted sender) smtp.mailfrom=hdanton@sina.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1674272843; a=rsa-sha256; cv=none; b=cY2ZYCZV032UJT7c1EVt1pdij9OyToSD/NhWt99CW+AgnI4qaKVpB0pp6HvbULngJFPTe8 OthNXBLqOxi1VTlHnF3NmeetFe6EaY0WH61642FxRmsp161rb5UMCBRqAbktIBaSyu6ko2 6DB4ddLG9I71P9fDJOduWU+gti9glCA= Received: from unknown (HELO localhost.localdomain)([114.249.61.130]) by sina.com (172.16.97.27) with ESMTP id 63CB5FCE00021B66; Sat, 21 Jan 2023 11:45:20 +0800 (CST) X-Sender: hdanton@sina.com X-Auth-ID: hdanton@sina.com X-SMAIL-MID: 37853349286477 From: Hillf Danton To: Sebastian Andrzej Siewior Cc: Mel Gorman , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Davidlohr Bueso , linux-mm@kvack.org, LKML Subject: Re: [PATCH v2] locking/rwbase: Prevent indefinite writer starvation Date: Sat, 21 Jan 2023 11:46:54 +0800 Message-Id: <20230121034654.3958-1-hdanton@sina.com> In-Reply-To: References: <20230117083817.togfwc5cy4g67e5r@techsingularity.net> <20230117165021.t5m7c2d6frbbfzig@techsingularity.net> <20230119011538.3247-1-hdanton@sina.com> <20230119135903.3524-1-hdanton@sina.com> <20230120093711.3862-1-hdanton@sina.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 1666110000D X-Stat-Signature: t8ccaqbq9y6yk7usy9xnujyyf4emfydg X-Rspam-User: X-HE-Tag: 1674272841-550323 X-HE-Meta: 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 H+mxepP+ zRhm04N5TfvrnGrD+Es81KIIfr0RCMxmgNA+Wb3qu4Ex8oJvi/2toH2cqrlw3TZAz0f8g0hon/UidQiY5CW4guiVX/s189tBEyjy/CwBdfwOrc8pMwZAGhwS+cen/kzyVzrqDHupXEceTtO3GJavxSt/K+aqh1Oa+UtRUjgGdU5xKgKmDQniDToGT18GOC87wga0LSMRvg1UUyGrgn+YyKHnrSxxFq9L/ekS5fV/W1XfB+m3UpSyeNLCPkA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.077047, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, 20 Jan 2023 19:34:02 +0100 Sebastian Andrzej Siewior > On 2023-01-20 17:37:11 [+0800], Hillf Danton wrote: > > > > I am fine with either 4ms or 40ms, or a second. > > > > Given the cure, does it still work when reader bias for RT tasks is allowed? > No. > > > If not, why keep starving waiters after they pay the 40ms price? > > That kind of starvation will also happen if you have only spinlock_t > locks and you say 3 RT tasks that acquire the lock back to back. And a > few SCHED_OTHER tasks. Those 3 will be always be in front of the queue > (as they skip the line) and the following SCHED_OTHER tasks will starve > and never get the lock. Given priority, what sense could be made by keeping RT task starved?