Re: [LSF/MM TOPIC] [ATTEND] Throttling I/O

[Suresh Jayaraman <sjayaraman@suse.com>]

On 01/25/2013 11:27 PM, Tejun Heo wrote:
> Hey, Suresh.
> 
> On Fri, Jan 25, 2013 at 06:49:34PM +0530, Suresh Jayaraman wrote:
>> - Making cfq schedule the per cgroup sync/async queues according to I/O
>>   weights would mean that we'll need to use per cgroup cfqq's instead
>>   of per process? What will the impact on sync latencies if for example
>>   we have many sync only tasks in one cgroup and many async tasks in
>>   another?  What if BLK_CGROUP is not configured, what would be the
>>   fallback behavior?
> 
> So, we currently have synd cfqqs in cgroup cfqgs and shared cfqqs in
> the root cfqg.  The end result would be splitting shared cfqqs into
> cgroup cfqgs.  We may have to change how cfqgs are chosen depending on
> whether it only has async IOs pending.  Not sure.

Ah, ok. Even if we have a way to check if in a particular cgroup all I/O
is async or not, I have feeling that sync latencies might still get
impacted for e.g. if we have a very few sync tasks plus many async tasks
in one cgroup competing with all sync tasks in another group or some
other combinations, no?


Thanks

-- 
Suresh Jayaraman