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[31.46.242.101]) by smtp.gmail.com with ESMTPSA id h4-20020a05600c350400b00402f713c56esm1165817wmq.2.2023.09.20.00.32.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 20 Sep 2023 00:32:41 -0700 (PDT) Sender: Ingo Molnar Date: Wed, 20 Sep 2023 09:32:38 +0200 From: Ingo Molnar To: Steven Rostedt Cc: Thomas Gleixner , Linus Torvalds , John Paul Adrian Glaubitz , Peter Zijlstra , Matthew Wilcox , Ankur Arora , linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org, akpm@linux-foundation.org, luto@kernel.org, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, mgorman@suse.de, jon.grimm@amd.com, bharata@amd.com, raghavendra.kt@amd.com, boris.ostrovsky@oracle.com, konrad.wilk@oracle.com, jgross@suse.com, andrew.cooper3@citrix.com, Geert Uytterhoeven , linux-m68k@lists.linux-m68k.org, Richard Weinberger , Anton Ivanov , Johannes Berg , linux-um@lists.infradead.org, Brian Cain , linux-hexagon@vger.kernel.org, Richard Henderson , Ivan Kokshaysky , Matt Turner , linux-alpha@vger.kernel.org Subject: Re: Arches that don't support PREEMPT Message-ID: References: <87cyyfxd4k.ffs@tglx> <87led2wdj0.ffs@tglx> <0e69f7df80dc5878071deb0d80938138d19de1d1.camel@physik.fu-berlin.de> <20230919134218.GA39281@noisy.programming.kicks-ass.net> <87pm2eui95.ffs@tglx> <20230919143816.1741760a@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230919143816.1741760a@gandalf.local.home> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Steven Rostedt wrote: > On Tue, 19 Sep 2023 20:31:50 +0200 > Thomas Gleixner wrote: > > > The removal of cond_resched() might cause latencies, but then I doubt > > that these museus pieces are used for real work :) > > We could simply leave the cond_resched() around but defined as nops for > everything but the "nostalgia club" to keep them from having any regressions. That's not a good idea IMO, it's an invitation for accelerated rate bitrot turning cond_resched() meaningless very quickly. We should remove cond_resched() - but probably not as the first step. They are conceptually independent of NEED_RESCHED_LAZY and we don't *have to* remove them straight away. By removing cond_resched() separately there's an easily bisectable point to blame for any longer latencies on legacy platforms, should any of them still be used with recent kernels. Thanks, Ingo