Messages in this thread | | | From | Thomas Gleixner <> | Subject | Re: [patch 18/20] posix-timers: Clarify posix_timer_fn() comments | Date | Thu, 01 Jun 2023 20:43:19 +0200 |
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On Thu, Jun 01 2023 at 15:21, Frederic Weisbecker wrote: > On Tue, Apr 25, 2023 at 08:49:24PM +0200, Thomas Gleixner wrote: >> Make the issues vs. SIG_IGN understandable and remove the 15 years old >> promise that a proper solution is already on the horizon. >> >> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> >> --- >> kernel/time/posix-timers.c | 56 +++++++++++++++++++++------------------------ >> 1 file changed, 27 insertions(+), 29 deletions(-) >> >> --- a/kernel/time/posix-timers.c >> +++ b/kernel/time/posix-timers.c >> @@ -325,11 +325,11 @@ int posix_timer_event(struct k_itimer *t >> } >> >> /* >> - * This function gets called when a POSIX.1b interval timer expires. It >> - * is used as a callback from the kernel internal timer. The >> - * run_timer_list code ALWAYS calls with interrupts on. >> - >> - * This code is for CLOCK_REALTIME* and CLOCK_MONOTONIC* timers. >> + * This function gets called when a POSIX.1b interval timer expires from >> + * the HRTIMER soft interrupt with interrupts enabled. > > BTW, what arranges for this to be called in softirq with interrupts enabled? > The modes I see used here are HRTIMER_MODE_ABS or HRTIMER_MODE_REL and not > their _SOFT counterparts.
Duh. My RT biased brain tricked me.
>> + * >> + * Handles CLOCK_REALTIME, CLOCK_MONOTONIC, CLOCK_BOOTTIME and CLOCK_TAI >> + * based timers. >> */ >> static enum hrtimer_restart posix_timer_fn(struct hrtimer *timer) >> { >> @@ -358,34 +359,31 @@ static enum hrtimer_restart posix_timer_ >> * FIXME: What we really want, is to stop this >> * timer completely and restart it in case the >> * SIG_IGN is removed. This is a non trivial >> - * change which involves sighand locking >> - * (sigh !), which we don't want to do late in >> - * the release cycle. >> + * change to the signal handling code. >> + * >> + * For now let timers with an interval less than a >> + * jiffie expire every jiffie to avoid softirq > > Or rather at least to the next jiffie, right? Because then in the next jiffie > it gets re-evaluated in case a real signal handler might have been set > in-between. > > Or it could be: > > + * For now let timers with an interval less than a > + * jiffie expire every jiffie (until a real sig handler > + * is found set) to avoid softirq...
Let me rephrase that.
>> + * starvation in case of SIG_IGN and a very small >> + * interval, which would put the timer right back >> + * on the softirq pending list. Moving now ahead of >> + * time tricks hrtimer_forward() to expire the >> + * timer later, while it still maintains the >> + * overrun accuracy for the price of a slightly >> + * inconsistency in the timer_gettime() case. This >> + * is at least better than a starved softirq. > [...] >> */ >> -#ifdef CONFIG_HIGH_RES_TIMERS >> - { >> + if (IS_ENABLED(CONFIG_HIGHRES_TIMERS)) { >> ktime_t kj = NSEC_PER_SEC / HZ; > > Could be TICK_NSECS?
Yep. Fixed it up.
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