From: David Laight <David.Laight@ACULAB.COM>
To: 'Tony Lindgren' <tony@atomide.com>,
Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Stephen Boyd <sboyd@kernel.org>,
Tomasz Figa <tomasz.figa@gmail.com>,
Sylwester Nawrocki <s.nawrocki@samsung.com>,
Will Deacon <will@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
Wolfram Sang <wsa+renesas@sang-engineering.com>,
Dejin Zheng <zhengdejin5@gmail.com>,
Kai-Heng Feng <kai.heng.feng@canonical.com>,
Nicholas Piggin <npiggin@gmail.com>,
Heiko Carstens <hca@linux.ibm.com>,
Peter Zijlstra <peterz@infradead.org>,
Russell King <linux@armlinux.org.uk>,
John Stultz <jstultz@google.com>,
Thomas Gleixner <tglx@linutronix.de>,
"Krzysztof Kozlowski" <krzk@kernel.org>,
Tero Kristo <tero.kristo@linux.intel.com>,
"Ulf Hansson" <ulf.hansson@linaro.org>,
"Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"linux-renesas-soc@vger.kernel.org"
<linux-renesas-soc@vger.kernel.org>,
"linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH v2 1/2] iopoll: Call cpu_relax() in busy loops
Date: Thu, 11 May 2023 10:48:37 +0000 [thread overview]
Message-ID: <494a000774b546e4aae00ae0a7dfeae4@AcuMS.aculab.com> (raw)
In-Reply-To: <20230511064839.GG14287@atomide.com>
From: Tony Lindgren
> Sent: 11 May 2023 07:49
>
> * Geert Uytterhoeven <geert+renesas@glider.be> [230510 13:23]:
> > It is considered good practice to call cpu_relax() in busy loops, see
> > Documentation/process/volatile-considered-harmful.rst. This can not
> > only lower CPU power consumption or yield to a hyperthreaded twin
> > processor, but also allows an architecture to mitigate hardware issues
> > (e.g. ARM Erratum 754327 for Cortex-A9 prior to r2p0) in the
> > architecture-specific cpu_relax() implementation.
Don't you also need to call cond_resched() (at least some times).
Otherwise the process can't be pre-empted and a RT process
that last ran on that cpu will never be scheduled.
David
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Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2023-05-11 10:49 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-10 13:23 [PATCH v2 0/2] iopoll: Busy loop and timeout improvements Geert Uytterhoeven
2023-05-10 13:23 ` [PATCH v2 1/2] iopoll: Call cpu_relax() in busy loops Geert Uytterhoeven
2023-05-11 6:48 ` Tony Lindgren
2023-05-11 10:48 ` David Laight [this message]
2023-05-23 7:29 ` Geert Uytterhoeven
2023-05-23 7:29 ` Geert Uytterhoeven
2023-05-23 8:55 ` David Laight
2023-05-23 8:55 ` David Laight
2023-05-11 9:48 ` Ulf Hansson
2023-05-10 13:23 ` [PATCH v2 2/2] iopoll: Do not use timekeeping in read_poll_timeout_atomic() Geert Uytterhoeven
2023-05-10 13:35 ` Arnd Bergmann
2023-05-10 13:46 ` Geert Uytterhoeven
2023-05-10 13:56 ` Arnd Bergmann
2023-05-11 6:48 ` Tony Lindgren
2023-05-11 10:26 ` Ulf Hansson
2023-05-11 12:44 ` Geert Uytterhoeven
2023-05-12 7:53 ` Ulf Hansson
2023-05-12 8:03 ` Geert Uytterhoeven
2023-05-15 9:26 ` Ulf Hansson
2023-05-15 9:26 ` Ulf Hansson
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