Messages in this thread | | | Date | Mon, 18 Apr 2016 15:39:56 -0400 | From | Waiman Long <> | Subject | Re: [PATCH -tip 2/3] locking/pvqspinlock: Avoid double resetting of stats |
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On 04/18/2016 02:31 AM, Davidlohr Bueso wrote: > ... remove the redundant second iteration, this is most > likely a copy/past buglet. > > Signed-off-by: Davidlohr Bueso<dbueso@suse.de> > --- > kernel/locking/qspinlock_stat.h | 2 -- > 1 file changed, 2 deletions(-) > > diff --git a/kernel/locking/qspinlock_stat.h b/kernel/locking/qspinlock_stat.h > index d734b7502001..72722334237a 100644 > --- a/kernel/locking/qspinlock_stat.h > +++ b/kernel/locking/qspinlock_stat.h > @@ -191,8 +191,6 @@ static ssize_t qstat_write(struct file *file, const char __user *user_buf, > > for (i = 0 ; i< qstat_num; i++) > WRITE_ONCE(ptr[i], 0); > - for (i = 0 ; i< qstat_num; i++) > - WRITE_ONCE(ptr[i], 0); > } > return count; > }
The double write is done on purpose. As the statistics count update isn't atomic, there is a very small chance (p) that clearing the count may happen in the middle of read-modify-write bus transaction. Doing a double write will reduce the chance further to p^2. This isn't failsafe, but I think is good enough.
However, I don't mind eliminate the double write either as we can always view the statistics count after a reset to make sure that they are properly cleared.
Cheers, Longman
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