Re: Dynamic switching of io_context
From: Vladislav Bolkhovitin
Date: Thu Dec 18 2008 - 08:47:37 EST
Jens Axboe, on 12/18/2008 04:40 PM wrote:
On Wed, Dec 17 2008, Vladislav Bolkhovitin wrote:
I haven't seen the rest of the code, so I may be wrong, but I suppose
that a better approach would be to use CLONE_IO to share io contexts,
if possible.
Unfortunately, it would be very non-optimal. As it is known, to achieve
the best performance with async. IO, it should be submitted by a limited
number of threads <= CPU count. So, the only way to submit IO from each
of, e.g. 100, clients in a dedicated per-client IO context is to
dynamically switch io_context of the current threads to io_context of
the client before IO submission.
There's also likely to be another use of exactly the same type of thing
- the acall patches from Zach. At least my vision of the punt-to-thread
approach would be very similar: grab an available thread and attach it
to a given IO context.
So while I did mention exactly what Fabio outlines in my initial mail on
this, a generic way to attach/detach IO contexts from processes/threads
would be useful outside of this project. nfsd comes to mind as well.
I fully agree. Looking forward to use that facility in 2.6.29! (I guess,
from your reference on Zach's patches, that the work is being done. If
I'm wrong and you need my participation in implementing it, just let me
know.)
Thanks,
Vlad
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