Re: [RFC] Block IO Controller V2 - some results

[Corrado Zoccolo]

Hi Vivek,
On Fri, Nov 20, 2009 at 3:18 PM, Vivek Goyal <vgoyal@xxxxxxxxxx> wrote:
> Hi Corrado,
>
> I liked the idea of putting all the sync-noidle queues together in root
> group to achieve better throughput and implemeted a small patch.
>
> It works fine for random readers. But when I do multiple direct random writers
> in one group vs a random reader in other group, I am getting strange
> behavior. Random reader moves to root group as sync-noidle workload. But
> random writers are largely sync queues in remain in other group. But many
> a times also jump into root group and preempt random reader.

can you try the attached patches?
They fix the problems you identified about no-idle preemption, and
deep seeky queues.
With those, you should not see this jumping any more.
I'll send them to Jens as soon has he comes back from vacation.

Corrado

> Anyway, with 4 random writers and 1 random reader running for 30 seconds
> in root group I get following.
>
> rw: 59,963KB/s
> rr: 66KB/s
>
> But if these are put in seprate groups test1 and test2 then
>
> rw: 30,587KB/s
> rr: 23KB/s
>
> I can understand the drop in rw throughput as it has been put under a
> group of weight 500. But rr will run in root group with weight 1000 and
> should have received much higher BW, instead it ends up loosing.
>
> Staring hard at blktrace output to figure out what's happening. One thing
> noticeable so far is that without cgroup stuff we seem to be interleaving
> dispatch from random reader and random writer much better as compared to
> with cgroup stuff.
>
> Thanks
> Vivek
>

Attachment: 0001-cfq-iosched-fix-no-idle-preemption-logic.patch
Description: Binary data

Attachment: 0002-cfq-iosched-idling-on-deep-seeky-sync-queues.patch
Description: Binary data