Cyril Hrubis 5fce29ab20 sched/rt: Fix sysctl_sched_rr_timeslice intial value ... [ Upstream commit c7fcb99877 ] There is a 10% rounding error in the intial value of the sysctl_sched_rr_timeslice with CONFIG_HZ_300=y. This was found with LTP test sched_rr_get_interval01: sched_rr_get_interval01.c:57: TPASS: sched_rr_get_interval() passed sched_rr_get_interval01.c:64: TPASS: Time quantum 0s 99999990ns sched_rr_get_interval01.c:72: TFAIL: /proc/sys/kernel/sched_rr_timeslice_ms != 100 got 90 sched_rr_get_interval01.c:57: TPASS: sched_rr_get_interval() passed sched_rr_get_interval01.c:64: TPASS: Time quantum 0s 99999990ns sched_rr_get_interval01.c:72: TFAIL: /proc/sys/kernel/sched_rr_timeslice_ms != 100 got 90 What this test does is to compare the return value from the sched_rr_get_interval() and the sched_rr_timeslice_ms sysctl file and fails if they do not match. The problem it found is the intial sysctl file value which was computed as: static int sysctl_sched_rr_timeslice = (MSEC_PER_SEC / HZ) * RR_TIMESLICE; which works fine as long as MSEC_PER_SEC is multiple of HZ, however it introduces 10% rounding error for CONFIG_HZ_300: (MSEC_PER_SEC / HZ) * (100 * HZ / 1000) (1000 / 300) * (100 * 300 / 1000) 3 * 30 = 90 This can be easily fixed by reversing the order of the multiplication and division. After this fix we get: (MSEC_PER_SEC * (100 * HZ / 1000)) / HZ (1000 * (100 * 300 / 1000)) / 300 (1000 * 30) / 300 = 100 Fixes: 975e155ed8 ("sched/rt: Show the 'sched_rr_timeslice' SCHED_RR timeslice tuning knob in milliseconds") Signed-off-by: Cyril Hrubis <chrubis@suse.cz> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Petr Vorel <pvorel@suse.cz> Acked-by: Mel Gorman <mgorman@suse.de> Tested-by: Petr Vorel <pvorel@suse.cz> Link: https://lore.kernel.org/r/20230802151906.25258-2-chrubis@suse.cz Signed-off-by: Sasha Levin <sashal@kernel.org>		2023-09-13 09:42:29 +02:00
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Makefile	…
autogroup.c	…
autogroup.h	…
build_policy.c	…
build_utility.c	…
clock.c	…
completion.c	…
core.c	cgroup/cpuset: Free DL BW in case can_attach() fails	2023-08-30 16:11:11 +02:00
core_sched.c	…
cpuacct.c	…
cpudeadline.c	…
cpudeadline.h	…
cpufreq.c	…
cpufreq_schedutil.c	…
cpupri.c	…
cpupri.h	…
cputime.c	…
deadline.c	sched/deadline: Create DL BW alloc, free & check overflow interface	2023-08-30 16:11:11 +02:00
debug.c	…
fair.c	sched/fair: Remove capacity inversion detection	2023-08-23 17:52:41 +02:00
features.h	…
idle.c	…
isolation.c	…
loadavg.c	…
membarrier.c	…
pelt.c	…
pelt.h	…
psi.c	sched/psi: use kernfs polling functions for PSI trigger polling	2023-07-27 08:50:38 +02:00
rt.c	sched/rt: Fix sysctl_sched_rr_timeslice intial value	2023-09-13 09:42:29 +02:00
sched-pelt.h	…
sched.h	sched/deadline: Create DL BW alloc, free & check overflow interface	2023-08-30 16:11:11 +02:00
smp.h	…
stats.c	…
stats.h	…
stop_task.c	…
swait.c	…
topology.c	…
wait.c	…
wait_bit.c	…