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From: Marcelo Tosatti <mtosatti@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Frederic Weisbecker <frederic@kernel.org>,
	"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] sched/idle: disable tick in idle=poll idle entry
Date: Fri, 9 Jun 2023 10:54:04 -0300	[thread overview]
Message-ID: <ZIMu/GzBZQ1EmiZ0@tpad> (raw)
In-Reply-To: <20230608083400.GH998233@hirez.programming.kicks-ass.net>

On Thu, Jun 08, 2023 at 10:34:00AM +0200, Peter Zijlstra wrote:
> On Wed, Jun 07, 2023 at 10:10:46PM -0300, Marcelo Tosatti wrote:
> > 
> > Commit a5183862e76fdc25f36b39c2489b816a5c66e2e5 
> > ("tick/nohz: Conditionally restart tick on idle exit") allows
> > a nohz_full CPU to enter idle and return from it with the 
> > scheduler tick disabled (since the tick might be undesired noise).
> > 
> > The idle=poll case still unconditionally restarts the tick when entering
> > idle.
> > 
> > To reduce the noise for that case as well, stop the tick when entering
> > idle, for the idle=poll case.
> > 
> > tick_nohz_idle_exit (called if the NEED_RESCHED bit is set) 
> > is responsible for re-enabling the tick when necessary. 
> 
> Who cares and why?

Systems that use isolcpus/nohz_full, and use idle=poll to avoid sleeping.
For example:

https://github.com/intel/FlexRAN/blob/master/README.md

More specifically, the case which HLTs (via nanosleep usually) is:

https://www.isa.org/intech-home/2022/february-2022/departments/what-you-may-not-know-about-softplcs

Can add this to the next version of the patch (unless you have any other
comments).

Thanks.


  reply	other threads:[~2023-06-09 19:44 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-06-08  1:10 [PATCH] sched/idle: disable tick in idle=poll idle entry Marcelo Tosatti
2023-06-08  8:34 ` Peter Zijlstra
2023-06-09 13:54   ` Marcelo Tosatti [this message]
2023-06-08 13:25 ` Frederic Weisbecker

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