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[109.81.84.7]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-483a9cab38dsm159620255e9.9.2026.02.23.01.11.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 23 Feb 2026 01:11:12 -0800 (PST) Date: Mon, 23 Feb 2026 10:11:11 +0100 From: Michal Hocko To: Marcelo Tosatti Cc: Vlastimil Babka , Leonardo Bras , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, Johannes Weiner , Roman Gushchin , Shakeel Butt , Muchun Song , Andrew Morton , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Vlastimil Babka , Hyeonggon Yoo <42.hyeyoo@gmail.com>, Leonardo Bras , Thomas Gleixner , Waiman Long , Boqun Feng , Frederic Weisbecker Subject: Re: [PATCH 0/4] Introduce QPW for per-cpu operations Message-ID: References: <3f2b985a-2fb0-4d63-9dce-8a9cad8ce464@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: zssh168ywh9117antqnqcxiz4yr1a8is X-Rspam-User: X-Rspamd-Queue-Id: 3960F1A000B X-Rspamd-Server: rspam01 X-HE-Tag: 1771837873-417214 X-HE-Meta: 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 3dW+nAjD W69g+H/esPs0tskoOKVdH62SStp7L4KmHp/u79h2jNRAi3zkhtpO8k9JwMPRcjm565gxZ6MwRxSeoh7qd4vxYiKHMhUfhH89jfukRxzBHWBrR7X1xLLOgg6xUtZIPUD2kcInSu1rnTXlK36s7qHFBZS2jLQDWdaHi5DFH6YLivxBc8ct7l2M18Hdyq8Rfr6m3QtmiKo4KnFegBt2gGhM85I3ZZw== 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 20-02-26 16:01:59, Marcelo Tosatti wrote: > On Fri, Feb 20, 2026 at 06:58:10PM +0100, Vlastimil Babka wrote: [...] > > >> So if we can assume that workloads on isolated cpus make syscalls only > > >> rarely, and when they do they can tolerate them being slower, I think the > > >> "avoid sheaves on isolated cpus" would be the best way here. > > > > > > I am not sure its safe to assume that. Ask Gemini about isolcpus use > > > cases and: > > > > I don't think it's answering the question about syscalls. But didn't read > > too closely given the nature of it. > > People use isolcpus with all kinds of programs. > > > > For example, AF_XDP bypass uses system calls (and wants isolcpus): > > > > > > https://www.quantvps.com/blog/kernel-bypass-in-hft?srsltid=AfmBOoryeSxuuZjzTJIC9O-Ag8x4gSwjs-V4Xukm2wQpGmwDJ6t4szuE > > > > Didn't spot system calls mentioned TBH. > > I don't see why you want to reduce performance of applications that > execute on isolcpus=, if you can avoid that. If you can avoid that by making performance bad for everybody else then then it seems safer to sacrifice those workloads that are much more special - i.e. cpu isolation. -- Michal Hocko SUSE Labs