From: Zach Brown <zach.brown@oracle.com>
To: Jeff Moyer <jmoyer@redhat.com>
Cc: user-mode-linux-devel@lists.sourceforge.net,
Miklos Szeredi <miklos@szeredi.hu>,
jdike@addtoit.com, linux-kernel@vger.kernel.org,
akpm@linux-foundation.org, torvalds@linux-foundation.org
Subject: Re: [uml-devel] [2.6.24 BUG] 100% iowait on host while UML is running
Date: Mon, 03 Dec 2007 10:53:21 -0800 [thread overview]
Message-ID: <475450A1.9000103@oracle.com> (raw)
In-Reply-To: <x49ir3fhg5n.fsf@segfault.boston.devel.redhat.com>
> We could check ctx->reqs_active before scheduling to determine whether
> or not we are waiting for I/O, but this would require taking the
> context lock in order to be accurate. Given that the test would be
> only for the sake of book keeping, it might be okay to do it outside
> of the lock.
>
> Zach, what are your thoughts on this?
I agree that it'd be OK to test it outside the lock, though we'll want
some commentary:
/* Try to only show up in io wait if there are ops in flight */
if (ctx->reqs_active)
io_schedule();
else
schedule();
It's cheap, safe, and accurate the overwhelming majority of the time :).
We only need it in read_events(). The other two io_schedule() calls are
only reached to wait on pending reqs specifically.
It still won't make sense for iocbs which aren't performing IO, but I
guess that's one more bridge to cross when we come to it.
Do you want to throw this tiny patch together and submit it?
- z
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WARNING: multiple messages have this Message-ID (diff)
From: Zach Brown <zach.brown@oracle.com>
To: Jeff Moyer <jmoyer@redhat.com>
Cc: Miklos Szeredi <miklos@szeredi.hu>,
akpm@linux-foundation.org, torvalds@linux-foundation.org,
jdike@addtoit.com, user-mode-linux-devel@lists.sourceforge.net,
linux-kernel@vger.kernel.org
Subject: Re: [2.6.24 BUG] 100% iowait on host while UML is running
Date: Mon, 03 Dec 2007 10:53:21 -0800 [thread overview]
Message-ID: <475450A1.9000103@oracle.com> (raw)
In-Reply-To: <x49ir3fhg5n.fsf@segfault.boston.devel.redhat.com>
> We could check ctx->reqs_active before scheduling to determine whether
> or not we are waiting for I/O, but this would require taking the
> context lock in order to be accurate. Given that the test would be
> only for the sake of book keeping, it might be okay to do it outside
> of the lock.
>
> Zach, what are your thoughts on this?
I agree that it'd be OK to test it outside the lock, though we'll want
some commentary:
/* Try to only show up in io wait if there are ops in flight */
if (ctx->reqs_active)
io_schedule();
else
schedule();
It's cheap, safe, and accurate the overwhelming majority of the time :).
We only need it in read_events(). The other two io_schedule() calls are
only reached to wait on pending reqs specifically.
It still won't make sense for iocbs which aren't performing IO, but I
guess that's one more bridge to cross when we come to it.
Do you want to throw this tiny patch together and submit it?
- z
next prev parent reply other threads:[~2007-12-03 18:54 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-12-03 15:32 [uml-devel] [2.6.24 BUG] 100% iowait on host while UML is running Miklos Szeredi
2007-12-03 15:32 ` Miklos Szeredi
2007-12-03 16:55 ` [uml-devel] " Jeff Moyer
2007-12-03 16:55 ` Jeff Moyer
2007-12-03 18:53 ` Zach Brown [this message]
2007-12-03 18:53 ` Zach Brown
2007-12-03 19:33 ` [uml-devel] " Jeff Moyer
2007-12-03 19:33 ` Jeff Moyer
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