Re: [RFC][PATCH 00/11] blkiocg async support

From: Munehiro Ikeda
Date: Wed Aug 04 2010 - 10:36:17 EST

Nauman Rafique wrote, on 08/03/2010 03:24 PM:
On Tue, Aug 3, 2010 at 7:31 AM, Munehiro Ikeda<m-ikeda@xxxxxxxxxxxxx> wrote:
Vivek Goyal wrote, on 08/02/2010 04:58 PM:
You will require one more piece and that is support for per cgroup request
descriptors on request queue. With writes, it is so easy to consume those
128 request descriptors.

Hi Vivek,

Yes. Thank you for the comment.
I have two concerns to do that.

(1) technical concern
If there is fixed device-wide limitation and there are so many groups,
the number of request descriptors distributed to each group can be too
few. My only idea for this is to make device-wide limitation flexible,
but I'm not sure if it is the best or even can be allowed.

(2) implementation concern
Now the limitation is done by generic block layer which doesn't know
about grouping. The idea in my head to solve this is to add a new
interface on elevator_ops to ask IO scheduler if a new request can
be allocated.

We have already done the work of forward porting the request
descriptor patch that Vivek had in his earlier patch sets. We also
taken care of the two concerns you have mentioned above. We have been
testing it, and getting good numbers. So if you want, I can send the
patch your way so it can be included in this same patch series.


Hi Nauman,

It is the patch that I'm thinking we should be based on. You have
already done the forward porting, great!
Please post it to LKML, container-list etc. independently if you don't
mind. I appreciate your suggestion to include it into my patch
series, but I'm worrying about that the patch set becomes larger
beyond my poor antique brain processor.
The issue of request limitation may be significant when async write is
supported, but I don't think it is limited to it. It should be
beneficial for current blkio controller.
And we can combine them after independent posts if needed.

Thanks a lot,

IKEDA, Munehiro
NEC Corporation of America

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