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Sun, 22 Mar 2026 17:51:38 -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, 22 Mar 2026 21:51:30 -0300 Message-ID: X-Mailer: git-send-email 2.53.0 In-Reply-To: <2d3ff0fc-17a2-4425-b949-b5100251f98e@kernel.org> References: <20260302154945.143996316@redhat.com> <20260302155105.214878062@redhat.com> <26662caf-de09-4f13-b374-dc7f879b7829@kernel.org> <2d3ff0fc-17a2-4425-b949-b5100251f98e@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 746B2100012 X-Stat-Signature: aps3enbjgi93hq9xjs66azzi1rty35iu X-Rspam-User: X-HE-Tag: 1774227101-302276 X-HE-Meta: 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 9SmqP7PL 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Mar 16, 2026 at 11:55:46AM +0100, Vlastimil Babka (SUSE) wrote: > On 3/15/26 18:37, Leonardo Bras wrote: > > 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=?, > > I'm not sure it's possible to achieve this ordering with __setup calls, > unless one of them is early, and then it might be too early to do the > necessary action. > > > so user could disable qpw if wanted. > > > > Would that work? > > The pattern I'm familiar with is collecting all related params via > early_param() setting some variables, and then an init call (not tied to any > of the param) looks at those variables and does whatever is necessary. > > > Thanks! > > Leo > > > > > > > Makes sense, will take a look on that approach. Thanks! Leo