Messages in this thread | | | Date | Wed, 15 Jul 2020 07:56:50 +0200 | From | "Ahmed S. Darwish" <> | Subject | Re: [PATCH v2 1/6] sched_clock: Expose struct clock_read_data |
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On Wed, Jul 15, 2020 at 10:05:07AM +0800, Leo Yan wrote: > From: Peter Zijlstra <peterz@infradead.org> > ... > > Provide struct clock_read_data and two (seqcount) helpers so that > architectures (arm64 in specific) can expose the numbers to userspace. > ... > > +struct clock_read_data *sched_clock_read_begin(unsigned int *seq) > +{ > + *seq = raw_read_seqcount(&cd.seq); > + return cd.read_data + (*seq & 1); > +} > + ...
Hmm, this seqcount_t is actually a latch seqcount. I know the original code also used raw_read_seqcount(), but while at it, let's use the proper read API for seqcount_t latchers: raw_read_seqcount_latch().
raw_read_seqcount_latch() has no read memory barrier though, and a suspicious claim that READ_ONCE() pairs with an smp_wmb() (??). But if its implementation is wrong, let's fix it there instead.
Thanks,
-- Ahmed S. Darwish Linutronix GmbH
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