XO-1.5 slow disk writes

Benjamin M. Schwartz bmschwar at fas.harvard.edu
Tue Nov 17 13:03:29 EST 2009

Daniel Drake wrote:
> Today I tried to figure out why running "sync" often takes 5-10 seconds
> or longer. This slows down suspend, where all data is synced to disk.

On the XO-1, it was necessary to sync before suspend, because there was no
guarantee that a suspended laptop would reawaken any time soon.  On 1.5
(and even on XO-1 with newer software) we should have fully working timed
wakeups.  That means the kernel could set a policy of a "sync every 5
minutes", and wake up out of suspend in order to perform the sync.  This
is, IMHO, actually better than a "sync on every suspend" policy, because
it enables things like write combining that improve performance and reduce
flash wear.

Of course, getting sync to be very fast would also be nice.


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