On Jan 10, 2008 12:13 AM, dean gaudet [off-list ref] wrote:

w.r.t. dan's cfq comments -- i really don't know the details, but does
this mean cfq will misattribute the IO to the wrong user/process?  or is
it just a concern that CPU time will be spent on someone's IO?  the latter
is fine to me... the former seems sucky because with today's multicore
systems CPU time seems cheap compared to IO.

I do not see this affecting the time slicing feature of cfq, because
as Neil says the work has to get done at some point.   If I give up
some of my slice working on someone else's I/O chances are the favor
will be returned in kind since the code does not discriminate.  The
io-priority capability of cfq currently does not work as advertised
with current MD since the priority is tied to the current thread and
the thread that actually submits the i/o on a stripe is
non-deterministic.  So I do not see this change making the situation
any worse.  In fact, it may make it a bit better since there is a
higher chance for the thread submitting i/o to MD to do its own i/o to
the backing disks.

Reviewed-by: Dan Williams <redacted>