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Tue, 10 Mar 2026 17:01:02 -0700 (PDT) From: Leonardo Bras To: "Vlastimil Babka (SUSE)" Cc: Leonardo Bras , Marcelo Tosatti , Michal Hocko , 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 , 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 Date: Tue, 10 Mar 2026 21:01:00 -0300 Message-ID: X-Mailer: git-send-email 2.53.0 In-Reply-To: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: 8bit X-Stat-Signature: dm318x1x9ak79a85d8j1owygjysg4oh7 X-Rspam-User: X-Rspamd-Queue-Id: 7BB9110000B X-Rspamd-Server: rspam12 X-HE-Tag: 1773187265-949308 X-HE-Meta: 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 c2g0ngVF D1mYrR84xoJPIUiFha+sTwFTMS+C4NfOB1jm3xTyA4goa2FQfiq8EF0hvyzNYYJ8COWetx6uHtGw5V807oiPt9grEF4B41Dtobxdo9aYjO6NoLUHUdxajOe1AtvewZ0HZNFpiuqDXkfvf9a8nfJRyrTxk0lPB4frtLUekB64HSN3rGErsFVOU4OTnfiN5tkrUkDqG4uLCoVDgf+kZqp62xr3wYN3xeIXgR/0CrET6pLDPcAemMmt9MKe6wyVGzeMrz0tJaIJwNsNShHw+KQpfz1tWrfAmaPpiAY6m/mlSiNsOAsNhsbM+qyC8KXPqPmfV9oJXjEGxVeFMaWfmLKiJX638avn+QHBiNaXrS2pXYNtWw6/hDXTtgOuucj0JLQDYCTv76dfd6UYLLbPqijhndbYXjkVDD3UjCNkJ+fnLOKC6Cww7SujenZWG0O1QVYa+eocatHdH63P6G4V2WIYfJL0qm3eYd5b7Q7YsOelG1ZtAYjeZtk7U8J86eEbBS6IU5ui64HF8xzhhJFYT+/8pOCdzCwEJq4zwwJnXklWgKV36ylabyxhtebpbzsqnpCRl+4IYA+XaByCFVJg= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Mar 09, 2026 at 10:52:55AM +0100, Vlastimil Babka (SUSE) wrote: > On 3/8/26 18:41, Leonardo Bras wrote: > > Hi Marcelo, > > > > Great, hiding migrate_disable under the static branch is the best scenario. > > > > I wonder why we spend 2 cycles on the static branches, though, should be > > close to nothing unless the branch predictor is too busy already. Well, we > > AFAIK static branches are runtime patched to non-conditional jumps or nops, > so there's nothing left for the branch predictor to do. Or maybe I > misunderstand your comment. > It does however increase code footprint and thus instruction cache usage, so > maybe that's an effect of that. Oh, I was not aware of that part. Since we can actually change the the branch decision variable in runtime, I guessed that it was just a optimized way for the processor to use the branch predictor. If it makes a non-conditional branch is even better then. Thanks! Leo > > > can always try to optimize in a different way. > > > > Thanks for the effort on this! > > Leo