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From: Peter Zijlstra <peterz@infradead.org>
To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Ingo Molnar <mingo@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Benson Leung <bleung@chromium.org>,
	Enric Balletbo i Serra <enric.balletbo@collabora.com>,
	Guenter Roeck <groeck@chromium.org>,
	Mark Brown <broonie@kernel.org>,
	linux-spi <linux-spi@vger.kernel.org>
Subject: Re: [PATCH 5/5] spi: Reduce kthread priority
Date: Thu, 1 Aug 2019 14:12:09 +0200	[thread overview]
Message-ID: <20190801121209.GD31381@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CAMuHMdU3D22PAWepGP6rMvDwJKVTfbxxH9J=kuo59PB7CCVKOA@mail.gmail.com>

On Thu, Aug 01, 2019 at 01:27:03PM +0200, Geert Uytterhoeven wrote:
> Hi Peter,
> 
> On Thu, Aug 1, 2019 at 1:18 PM Peter Zijlstra <peterz@infradead.org> wrote:
> > The SPI thingies request FIFO-99 by default, reduce this to FIFO-50.
> >
> > FIFO-99 is the very highest priority available to SCHED_FIFO and
> > it not a suitable default; it would indicate the SPI work is the
> > most important work on the machine.
> >
> > Cc: Benson Leung <bleung@chromium.org>
> > Cc: Enric Balletbo i Serra <enric.balletbo@collabora.com>
> > Cc: Guenter Roeck <groeck@chromium.org>
> > Cc: Mark Brown <broonie@kernel.org>
> > Cc: linux-spi@vger.kernel.org
> > Cc: linux-kernel@vger.kernel.org
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> > ---
> >  drivers/platform/chrome/cros_ec_spi.c |    2 +-
> >  drivers/spi/spi.c                     |    2 +-
> >  2 files changed, 2 insertions(+), 2 deletions(-)
> >
> > --- a/drivers/platform/chrome/cros_ec_spi.c
> > +++ b/drivers/platform/chrome/cros_ec_spi.c
> > @@ -706,7 +706,7 @@ static int cros_ec_spi_devm_high_pri_all
> >                                            struct cros_ec_spi *ec_spi)
> >  {
> >         struct sched_param sched_priority = {
> > -               .sched_priority = MAX_RT_PRIO - 1,
> > +               .sched_priority = MAX_RT_PRIO / 2,
> 
> include/linux/sched/prio.h says:
> 
>  * Priority of a process goes from 0..MAX_PRIO-1, valid RT
>  * priority is 0..MAX_RT_PRIO-1, and SCHED_NORMAL/SCHED_BATCH
>  * tasks are in the range MAX_RT_PRIO..MAX_PRIO-1. Priority
>  * values are inverted: lower p->prio value means higher priority.
> 
> So the new 50 is actually a higher priority than the old 99?
> 
> Given I'm far from an RT expert, I must be missing something?
> Thanks!

Ah; you found the confusion ;-)

https://lkml.kernel.org/20190617122448.GA3436@hirez.programming.kicks-ass.net

But basically, user-space prio is [1-99], while in-kernel prio is
[0-98]. The above is user prio (it basically uses the
sched_setscheduler() syscall).

So 50 really is lower than 99.

  reply	other threads:[~2019-08-01 12:12 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-01 11:13 [PATCH 0/5] Fix FIFO-99 abuse Peter Zijlstra
2019-08-01 11:13 ` [PATCH 1/5] sched/pci: Reduce psimon FIFO priority Peter Zijlstra
2019-08-01 17:49   ` Johannes Weiner
2019-08-01 18:31     ` Suren Baghdasaryan
2019-08-01 21:03       ` Suren Baghdasaryan
2019-08-01 21:02     ` Peter Zijlstra
2019-08-01 11:13 ` [PATCH 2/5] rcu/tree: Fix SCHED_FIFO params Peter Zijlstra
2019-08-01 13:51   ` Paul E. McKenney
2019-08-01 14:43     ` Peter Zijlstra
2019-08-01 15:33       ` Paul E. McKenney
2019-08-01 11:13 ` [PATCH 3/5] crypto: Reduce default RT priority Peter Zijlstra
2019-08-09  6:19   ` Herbert Xu
2019-08-01 11:13 ` [PATCH 4/5] media/ivtv: Reduce default FIFO priority Peter Zijlstra
2019-08-01 12:24   ` Andy Walls
2019-08-01 12:38     ` Peter Zijlstra
2019-08-02  8:58       ` Peter Zijlstra
2019-08-07  9:26         ` Hans Verkuil
2019-08-01 11:13 ` [PATCH 5/5] spi: Reduce kthread priority Peter Zijlstra
2019-08-01 11:26   ` Mark Brown
2019-08-01 12:07     ` Peter Zijlstra
2019-08-01 11:27   ` Geert Uytterhoeven
2019-08-01 12:12     ` Peter Zijlstra [this message]
2019-08-01 12:16       ` Geert Uytterhoeven
2019-08-01 11:27   ` Enric Balletbo i Serra
2019-08-01 12:17     ` Peter Zijlstra
2019-08-01 12:35       ` Mark Brown
2019-08-01 15:44         ` Doug Anderson
2019-08-02 11:22   ` Applied "spi: Reduce kthread priority" to the spi tree Mark Brown
2019-08-02 11:22     ` Mark Brown
2019-08-01 13:17 ` [PATCH 0/5] Fix FIFO-99 abuse Qais Yousef
2019-08-02  9:32   ` Peter Zijlstra
2019-08-02  9:50     ` Thomas Gleixner
2019-08-02 10:26     ` Qais Yousef
2019-08-02 12:41       ` Peter Zijlstra
2019-08-02 14:08         ` Qais Yousef
2019-08-02 14:33           ` Peter Zijlstra
2019-08-02 15:21             ` Qais Yousef

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