Le Wed, Sep 11, 2024 at 07:13:39AM +0200, Anna-Maria Behnsen a écrit :
> When commit 38f7b7067dae ("powerpc/rtas: rtas_busy_delay() improvements")
> was introduced, documentation about proper usage of sleep realted functionsrelated* > was outdated. > > The commit message references the usage of a HZ=100 system. When using a > 20ms sleep duration on such a system and therefore using msleep(), the > possible additional slack will be +10ms. > > When the system is configured with HZ=100 the granularity of a jiffy and of > a bucket of the lowest timer wheel level is 10ms. To make sure a timer will > not expire early (when queueing of the timer races with an concurrent > update of jiffies), timers are always queued into the next bucket. This is > the reason for the maximal possible slack of 10ms. > > fsleep() limits the maximal possible slack to 25% by making threshold > between usleep_range() and msleep() HZ dependent. As soon as the accuracy > of msleep() is sufficient, the less expensive timer list timer based > sleeping function is used instead of the more expensive hrtimer based > usleep_range() function. The udelay() will not be used in this specific > usecase as the lowest sleep length is larger than 1 microsecond. Isn't udelay() for everything below 10us ? > > Use fsleep() directly instead of using an own heuristic for the best > sleeping mechanism to use.. > > Cc: Michael Ellerman <m...@ellerman.id.au> > Cc: Nathan Lynch <nath...@linux.ibm.com> > Cc: linuxppc-dev@lists.ozlabs.org > Signed-off-by: Anna-Maria Behnsen <anna-ma...@linutronix.de> > Acked-by: Michael Ellerman <m...@ellerman.id.au> (powerpc) Reviewed-by: Frederic Weisbecker <frede...@kernel.org>
