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Sun, 15 Mar 2026 10:37:39 -0700 (PDT) From: Leonardo Bras To: "Vlastimil Babka (SUSE)" Cc: Leonardo Bras , Marcelo Tosatti , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , Muchun Song , Andrew Morton , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Hyeonggon Yoo <42.hyeyoo@gmail.com>, Thomas Gleixner , Waiman Long , Boqun Feun , Frederic Weisbecker Subject: Re: [PATCH v2 2/5] Introducing qpw_lock() and per-cpu queue & flush work Date: Sun, 15 Mar 2026 14:37:29 -0300 Message-ID: X-Mailer: git-send-email 2.53.0 In-Reply-To: <26662caf-de09-4f13-b374-dc7f879b7829@kernel.org> References: <20260302154945.143996316@redhat.com> <20260302155105.214878062@redhat.com> <26662caf-de09-4f13-b374-dc7f879b7829@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 5289740008 X-Rspamd-Server: rspam07 X-Stat-Signature: 13h9cbw4arw668tbb6695t3wm8dn9odz X-Rspam-User: X-HE-Tag: 1773596262-855558 X-HE-Meta: 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 MDygcSRH vSQyhdNKA0DKk+6DAglwO1RlzunwOfAZ4gB/nKnTsAyKe8YGvz9LfCWRK3wHRhu/8DrPev/3dAYWCoEuf2PUFWDZto6KB9yFscP77S66SWagAWdpzKvB3XVj9qFXdni3nJbQMO3/oJl3z9XgMrjOVJj4jTzM1dOVM+8AKflA8mf5fpKQgUbHtjG2uWojLuhc9vsIrO94xzfvgr8OsB0FOsaqYKv0nOtwjPaxikmjQDabjlg8M+3KKU05AOSB0vNmIO7DtlaoLavlXg+rgh//c8XZpIeeeTu4PWjlIcEGPP4CRxICuNOgHFQvVcuk8LY6ToRKB33ytgyAPtOMbT59+MswclikqXTi1Mm1AIphi736VWItsT/IfytmiS9BiUWsiUX/7xfHR6LMIFAmtDpqFIVHGiUt/Qj6sFzjfRHYHlUBGyUUBfPyrQQs3OwiWGi6avhLrDXISoVvrerHLf03qO9qnf8JfA1j0athREiBYyUKw49OOKlh+XmrtboxILiHe5KnF27KXQp9cVOv/SzqQfMAMNmL6SkveWg2hEzOLeeunbTuzkenZBNx6XMCypJKwoRihQTt+tKpUJgkI6dOgclRGh+zxvLqZxCMKi4xZ/92MAZmoy4TfYYzy859SyiuScbtX Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Mar 11, 2026 at 08:58:05AM +0100, Vlastimil Babka (SUSE) wrote: > On 3/2/26 16:49, Marcelo Tosatti wrote: > > Index: linux/Documentation/admin-guide/kernel-parameters.txt > > =================================================================== > > --- linux.orig/Documentation/admin-guide/kernel-parameters.txt > > +++ linux/Documentation/admin-guide/kernel-parameters.txt > > @@ -2840,6 +2840,16 @@ Kernel parameters > > > > The format of is described above. > > > > + qpw= [KNL,SMP] Select a behavior on per-CPU resource sharing > > + and remote interference mechanism on a kernel built with > > + CONFIG_QPW. > > + Format: { "0" | "1" } > > + 0 - local_lock() + queue_work_on(remote_cpu) > > + 1 - spin_lock() for both local and remote operations > > + > > + Selecting 1 may be interesting for systems that want > > + to avoid interruption & context switches from IPIs. > Requiring a new boot option is always a nuissance. The cpu isolation is > AFAIK difficult enough to setup already. Could the default be that qpw will > auto-enable if there are isolated cpus configured? The option could still be > useful for overriding that automatic decision to both 0 and 1 for testing > etc, but not requried for the expected usecase? I think it's okay, as something like this? (should work for nohz_full and isolcpus) ###### diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c index 81bc8b329ef17..6c9052c28e3e4 100644 --- a/kernel/sched/isolation.c +++ b/kernel/sched/isolation.c @@ -170,20 +170,23 @@ static int __init housekeeping_setup(char *str, unsigned long flags) for_each_set_bit(type, &iter_flags, HK_TYPE_MAX) housekeeping_setup_type(type, housekeeping_staging); } if ((flags & HK_FLAG_KERNEL_NOISE) && !(housekeeping.flags & HK_FLAG_KERNEL_NOISE)) tick_nohz_full_setup(non_housekeeping_mask); housekeeping.flags |= flags; err = 1; + if (IS_ENABLED(CONFIG_QPW_DEFAULT)) + qpw_setup("1"); + free_housekeeping_staging: free_bootmem_cpumask_var(housekeeping_staging); free_non_housekeeping_mask: free_bootmem_cpumask_var(non_housekeeping_mask); return err; } ###### We would only have to be sure that this runs before cmdline parses qpw=?, so user could disable qpw if wanted. Would that work? Thanks! Leo