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Thu, 26 Oct 2023 14:58:58 -0400 (EDT) Message-ID: <7871472b-a0c4-4475-9671-69a3244f956d@efficios.com> Date: Thu, 26 Oct 2023 14:59:13 -0400 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [POC][RFC][PATCH v2] sched: Extended Scheduler Time Slice Content-Language: en-US To: Linus Torvalds Cc: Steven Rostedt , Peter Zijlstra , LKML , Thomas Gleixner , Ankur Arora , 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, 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 , Youssef Esmat , Vineeth Pillai , Suleiman Souhlal , Ingo Molnar , Daniel Bristot de Oliveira References: <20231025235413.597287e1@gandalf.local.home> <20231026105944.GJ33965@noisy.programming.kicks-ass.net> <20231026071413.4ed47b0e@gandalf.local.home> From: Mathieu Desnoyers In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: C3C1C4000E X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: u5jkz97u81bz3pbbpi775y1inxgmacuw X-HE-Tag: 1698346739-476484 X-HE-Meta: U2FsdGVkX1/w5oyH9INs2TzKLpR3WyXXPNP0mmtYtTSUIbOb9dyi2HrE75H9Gw8FtXkIjPW+ez4CMwKk6+1ZCsL6b2GGEzPplVZbWPpd+wDODwlWRXoShqE6rMt5pGxBDH/V/aiqJ49sAXPKTEavnm3JwhCyADjAOYGH7bdyTgWLb2/T5WtmgvBjfyGTBMrrksB9XLxu6wvXVJQntpmzTyBi0dFwETiGjzzBduKcokviSTq13ivylpaveHEfXfAyOGUjMVipOLkaCCgK2aDYsaIYSVGxcxeTQAhKsf8r1eApqMGtmGSuu5WCeiK03E5TTrwxHh7dcknE2x54+P/X4TLnd+Dno1O041OhoYTOtjuCcfYa9Re8+5yV6ijuCbBwPeHs1WNy20wRuA18FhXBZif1nVTdwDk0vgLtGtGSgbwyEgRR9j1ID2nEkFR5eHQ2Qf5/JoPGnBhU826APlkC5id3A4DunOgnCU07l0D3vUmfmhKzw7AznqGKYw0YdEe1ZIW+vO7zumcYlxOu7oXk/CSlyMKuoeeBWnJuBKlpPncoUvqMVVLeaEN/wGsGKErtYfMZsV4Y75efz59maA0UwetB/G5Te4wTKmQ6nW+V3n3yPhvDYng7+9Yb8Pvru7nAz9DUSqEMmsWmDGY3b4UEa92hIxVKDH9ua/x6iIGY1ouhXUahb4IJ6AxG7Lb0wNy+kZkCYs6meWf1ePqzFBhKK4g7mDBol4H0CNU/CLYtehE9ngLgh7NfjDcjTLp48GM4zEEIoCRsR/U4XqdUv3GC66fJqYdfoO4efrCMbfmp8JMfyK+A83Z5Bmi0mU6A4x5dN0eMk/3xoHD7d0ObSD1coee0fvYWxV0d/XKCLr03iOFe7bAAOO5/Gc6a0dF9ypUhAGWMPZ/uS0cUYXSmS/gcFpzjB1IVaCkJEqjQCmTfZ2YhvsYAzlQCGQkOhP2emUv/LOHuNU+IXNzCPPVB9xr XWE0NwZR 81K8ZO9q+nWiiLGGx2vXOjA0iS4k3ebUu6/6KYkX9s9NNhnODzAgtCTIrHOBprVA/3v2TsO4xOTtUVsf+Cwi7cFPc+IC9luBOf3yDrQcD+aMh4cbDUQF9szpYpB9HcSGDvvr7pcmsjANg5NTDU/QmkDP59BZpWWRcQKUhRmlp9a7EESRo3Jd0nW00JYYhameZX3AC/jNpZLu1Qvau0yE9RrefW4YtliDVWiBVrquFkUhRq5OgmYZefO1HQp20klj250YPVPIsSlQ8x2WR8k90et8rPBYjG2+jFsPntXIxXBmz07JEr0RBus3HXzv8QeXmwO4lXILgtedLC6jt60fcr8pkuJJQnrG5GHqO 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 2023-10-26 14:50, Linus Torvalds wrote: > On Thu, 26 Oct 2023 at 08:36, Mathieu Desnoyers > wrote: >> >>> asm volatile("xchg %b0,%1" >> >> which has an implicit lock prefix (xchg with a memory operand is a >> special-case): > > Yeah, this is why we do "percpu_xchg()" - which does not want locked > semantics - as a "cmpxchg" loop. > > Steven, check out > > arch/x86/include/asm/percpu.h > > for a rough implementation of a 'xchg()' without SMP coherency, just > cpu-local one (ie atomic wrt being preempted by the kernel, but not > atomic wrt other CPU's accessing the same variable concurrently) Actually Steven does not need a xchg to test-and-set a single bit which is only accessed concurrently between kernel and userspace from the same thread. Either "bts" or "andb" should work fine. Thanks, Mathieu > > Linus -- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com