linux-kernel - Re: [PATCH v2] sched/isolation: Make use of more than one housekeeping cpu

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Message-ID: <20250321081604.GA103187@pauld.westford.csb>
Date: Fri, 21 Mar 2025 09:16:04 +0100
From: Phil Auld <pauld@...hat.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Waiman Long <llong@...hat.com>, Ingo Molnar <mingo@...hat.com>,
	linux-kernel@...r.kernel.org, Juri Lelli <juri.lelli@...hat.com>,
	Vishal Chourasia <vishalc@...ux.ibm.com>,
	Vineeth Reddy <vineethr@...ux.ibm.com>,
	Frederic Weisbecker <frederic@...nel.org>
Subject: Re: [PATCH v2] sched/isolation: Make use of more than one
 housekeeping cpu

Hi Peter,

On Fri, Mar 14, 2025 at 07:38:22PM -0400 Waiman Long wrote:
> On 3/5/25 12:14 PM, Phil Auld wrote:
> > On Tue, Mar 04, 2025 at 02:24:19PM +0100 Frederic Weisbecker wrote:
> > > Le Tue, Feb 18, 2025 at 06:46:18PM +0000, Phil Auld a écrit :
> > > > The exising code uses housekeeping_any_cpu() to select a cpu for
> > > > a given housekeeping task. However, this often ends up calling
> > > > cpumask_any_and() which is defined as cpumask_first_and() which has
> > > > the effect of alyways using the first cpu among those available.
> > > > 
> > > > The same applies when multiple NUMA nodes are involved. In that
> > > > case the first cpu in the local node is chosen which does provide
> > > > a bit of spreading but with multiple HK cpus per node the same
> > > > issues arise.
> > > > 
> > > > We have numerous cases where a single HK cpu just cannot keep up
> > > > and the remote_tick warning fires. It also can lead to the other
> > > > things (orchastration sw, HA keepalives etc) on the HK cpus getting
> > > > starved which leads to other issues.  In these cases we recommend
> > > > increasing the number of HK cpus.  But... that only helps the
> > > > userspace tasks somewhat. It does not help the actual housekeeping
> > > > part.
> > > > 
> > > > Spread the HK work out by having housekeeping_any_cpu() and
> > > > sched_numa_find_closest() use cpumask_any_and_distribute()
> > > > instead of cpumask_any_and().
> > > > 
> > > > Signed-off-by: Phil Auld <pauld@...hat.com>
> > > > Reviewed-by: Waiman Long <longman@...hat.com>
> > > > Cc: Peter Zijlstra <peterz@...radead.org>
> > > > Cc: Juri Lelli <juri.lelli@...hat.com>
> > > > Cc: Frederic Weisbecker <frederic@...nel.org>
> > > > Cc: Waiman Long <longman@...hat.com>
> > > > Cc: linux-kernel@...r.kernel.org
> > > > Link: https://lore.kernel.org/lkml/20250211141437.GA349314@pauld.westford.csb/
> > > Acked-by: Frederic Weisbecker <frederic@...nel.org>
> > > 
> > Thanks Frederic!
> > 
> > Anyone with commit powers willing to pick this up?
> 
> Is this patch eligible to be merged into sched/core for the current cycle or
> will have to wait until the next one?
> 
> Thanks,
> Longman
> 

This is the patch (in this thread somewhere...) I mentioned the other
day at OSPM. 

Thanks!


Cheers,
Phil

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