Messages in this thread | ![/](/images/icornerl.gif) | | From | Arun KS <> | Date | Mon, 24 Jul 2023 10:07:28 +0530 | Subject | Re: Question on sched_clock |
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On Thu, Jul 20, 2023 at 4:07 PM Peter Zijlstra <peterz@infradead.org> wrote: > > On Thu, Jul 20, 2023 at 03:54:56PM +0530, Arun KS wrote: > > CCing maintainers > > > > On Wed, Jul 19, 2023 at 10:36 AM Arun KS <arunks.linux@gmail.com> wrote: > > > > > > Hi, > > > > > > Kernel’s printk uses local_clock() for timestamps and it is mapped to > > > sched_clock(). Two problems/requirements I see, > > > > > > One, Kernel’s printk timestamps start from 0, I want to change this to > > > match with actual time since boot. > > You can fundamentally only consistently tell time since the clock gets > initialized. Starting at 0 is what you get. > > > > Two, sched_clock() doesn’t account for time spend in low power > > > state(suspend to ram) > > Why would we do that? The next person will complain that they don't want > this. Then another person complains they also want time spend in > suspend-to-disk, and another person wants a pony.
Thanks Peter, Got your point. I was trying to understand if there are any other side effects of doing this downstream.
> > > > > > > Could workout patches to modify these behaviours and found working in > > > my system. But need to hear expert opinion on why this is not done in > > > the upstream. > > > > > > diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c > > > index 68d6c1190ac7..b63b2ded5727 100644 > > > --- a/kernel/time/sched_clock.c > > > +++ b/kernel/time/sched_clock.c > > This is only one of many sched_clock implementations... > > > > @@ -190,7 +190,10 @@ sched_clock_register(u64 (*read)(void), int bits, > > > unsigned long rate) > > > /* Update epoch for new counter and update 'epoch_ns' from old counter*/ > > > new_epoch = read(); > > > cyc = cd.actual_read_sched_clock(); > > > - ns = rd.epoch_ns + cyc_to_ns((cyc - rd.epoch_cyc) & > > > rd.sched_clock_mask, rd.mult, rd.shift); > > > + if (!cyc) > > > + ns = cyc_to_ns(new_epoch, new_mult, new_shift) > > > + else > > > + ns = rd.epoch_ns + cyc_to_ns((cyc - rd.epoch_cyc) & > > > rd.sched_clock_mask, rd.mult, rd.shift); > > > cd.actual_read_sched_clock = read; > > > > > > rd.read_sched_clock = read; > > > > > > @@ -287,7 +290,6 @@ void sched_clock_resume(void) > > > { > > > struct clock_read_data *rd = &cd.read_data[0]; > > > > > > - rd->epoch_cyc = cd.actual_read_sched_clock(); > > And what if you've been suspended long enough to wrap the clock ?!? Fair point. Will take a note.
> > > > hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL_HARD); > > > rd->read_sched_clock = cd.actual_read_sched_clock; > > > } > > > > > > Regards, > > > Arun
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