diff options
| author | Heiko Carstens <hca@linux.ibm.com> | 2026-02-18 15:20:06 +0100 |
|---|---|---|
| committer | Vasily Gorbik <gor@linux.ibm.com> | 2026-02-25 16:46:07 +0100 |
| commit | aefa6ec890f0d39a89fc80e95908ec1996337eee (patch) | |
| tree | 4c4c5a405bda1fb44564d27a05b41d6f9171da76 | |
| parent | dbc0fb35679ed5d0adecf7d02137ac2c77244b3b (diff) | |
| download | linux-aefa6ec890f0d39a89fc80e95908ec1996337eee.tar.gz linux-aefa6ec890f0d39a89fc80e95908ec1996337eee.zip | |
s390/idle: Add comment for non obvious code
Add a comment to update_timer_idle() which describes why wall time (not
steal time) is added to steal_timer. This is not obvious and was reported
by Frederic Weisbecker.
Reported-by: Frederic Weisbecker <frederic@kernel.org>
Closes: https://lore.kernel.org/all/aXEVM-04lj0lntMr@localhost.localdomain/
Reviewed-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
| -rw-r--r-- | arch/s390/kernel/idle.c | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/arch/s390/kernel/idle.c b/arch/s390/kernel/idle.c index 0f9e53f0a068..4e09f126d4fc 100644 --- a/arch/s390/kernel/idle.c +++ b/arch/s390/kernel/idle.c @@ -34,6 +34,15 @@ void update_timer_idle(void) this_cpu_add(mt_cycles[i], cycles_new[i] - idle->mt_cycles_enter[i]); } + /* + * This is a bit subtle: Forward last_update_clock so it excludes idle + * time. For correct steal time calculation in do_account_vtime() add + * passed wall time before idle_enter to steal_timer: + * During the passed wall time before idle_enter CPU time may have + * been accounted to system, hardirq, softirq, etc. lowcore fields. + * The accounted CPU times will be subtracted again from steal_timer + * when accumulated steal time is calculated in do_account_vtime(). + */ lc->steal_timer += idle->clock_idle_enter - lc->last_update_clock; lc->last_update_clock = lc->int_clock; |