Messages in this thread | | | Date | Wed, 4 Feb 2015 17:23:51 -0800 | From | Stephen Boyd <> | Subject | Re: [PATCH v3 4/4] sched_clock: Avoid deadlock during read from NMI |
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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?
> +{ > + /* 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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