Messages in this thread | | | Date | Wed, 4 Feb 2015 20:48:38 -0500 | From | Steven Rostedt <> | Subject | Re: [PATCH v3 4/4] sched_clock: Avoid deadlock during read from NMI |
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On Wed, 4 Feb 2015 17:23:51 -0800 Stephen Boyd <sboyd@codeaurora.org> wrote:
> On 01/30, Daniel Thompson wrote: > > @@ -98,26 +98,50 @@ unsigned long long notrace sched_clock(void) > > } > > > > /* > > + * Updating the data required to read the clock. > > + * > > + * sched_clock will never observe mis-matched data even if called from > > + * an NMI. We do this by maintaining an odd/even copy of the data and > > + * steering sched_clock to one or the other using a sequence counter. > > + * In order to preserve the data cache profile of sched_clock as much > > + * as possible the system reverts back to the even copy when the update > > + * completes; the odd copy is used *only* during an update. > > + */ > > +static void update_clock_read_data(struct clock_read_data *rd) > > notrace?
Why? Isn't this for update, not for readers?
-- Steve
> > > +{ > > + /* update the backup (odd) copy with the new data */ > > + cd.read_data[1] = *rd; > > + > > + /* steer readers towards the new data */ > > s/new data/odd copy/? > > > + raw_write_seqcount_latch(&cd.seq); > > + > > + /* now its safe for us to update the normal (even) copy */ > > + cd.read_data[0] = *rd; > > + > > + /* switch readers back to the even copy */ > > + raw_write_seqcount_latch(&cd.seq); > > +} > > + > > +/* > > >
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