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Received: from 77-249-17-89.cable.dynamic.v4.ziggo.nl ([77.249.17.89] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.98 #2 (Red Hat Linux)) id 1teC9T-0000000FxRh-2GuG; Sat, 01 Feb 2025 11:59:07 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 1E7DE30050D; Sat, 1 Feb 2025 12:59:07 +0100 (CET) Date: Sat, 1 Feb 2025 12:59:06 +0100 From: Peter Zijlstra To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, Thomas Gleixner , Ankur Arora , Linus Torvalds , 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, juri.lelli@redhat.com, vincent.guittot@linaro.org, willy@infradead.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, Joel Fernandes , Vineeth Pillai , Suleiman Souhlal , Ingo Molnar , Mathieu Desnoyers , Clark Williams , bigeasy@linutronix.de, daniel.wagner@suse.com, joseph.salisbury@oracle.com, broonie@gmail.com Subject: Re: [RFC][PATCH 1/2] sched: Extended scheduler time slice Message-ID: <20250201115906.GB8256@noisy.programming.kicks-ass.net> References: <20250131225837.972218232@goodmis.org> <20250131225942.365475324@goodmis.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250131225942.365475324@goodmis.org> X-Rspamd-Queue-Id: 04CB7140005 X-Stat-Signature: 8jwdfgxwk9b1y886h7s8j1dobi7qjrs3 X-Rspam-User: X-Rspamd-Server: rspam12 X-HE-Tag: 1738411157-114958 X-HE-Meta: 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 AIPf5pXq //l+XXPKMafCGnsgmWTovr4Jvv+gNc04UDBzyRdgOnAeucNgaqT2+d1o4vYeQjjVUdDKf13ljc6tbCxlS3FV+AgBKQynqROIb1CiIsX6Nnj/01J/6Zt0wRqkE+DsAUsW1O//gVSbZLjkQOTAjZ1nmBHjgNhieL/b0Vv2b0Vfq+qwpcTtgCcWC2cCfpwM0gxTB62K/02ipBB2MPifforChOK+O/X9qb5J2Qjyg9Zno2/o6KkvdcInacG5M+jnntHtzkXbRbG36xPqhaCxtVkpH0IMXmijkiXAElo8DiyRAQgATEYzJFbpdtOMrrBXCvVaVyJQa X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Jan 31, 2025 at 05:58:38PM -0500, Steven Rostedt wrote: > From: "Steven Rostedt (Google)" > > This is to improve user space implemented spin locks or any critical > section. It may also be extended for VMs and their guest spin locks as > well, but that will come later. > > This adds a new field in the struct rseq called cr_counter. This is a 32 bit > field where bit zero is a flag reserved for the kernel, and the other 31 > bits can be used as a counter (although the kernel doesn't care how they > are used, as any bit set means the same). > > This works in tandem with PREEMPT_LAZY, where a task can tell the kernel > via the rseq structure that it is in a critical section (like holding a > spin lock) that it will be leaving very shortly, and to ask the kernel to > not preempt it at the moment. I still have full hate for this approach.