Re: [PATCH] Btrfs: fix submit_worker congestion

[Chris Mason <chris.mason@xxxxxxxxxx>]

On Tue, Nov 29, 2011 at 09:40:56PM +0100, Arne Jansen wrote:
> Write bios are submitted from the submit_worker. The worker pumps down
> bios into the block layer until it signals a congestion. At least this
> is the theory. In pratice submit_bio just blocks before any signalling
> happens. As the bios are queued per device, this can lead to a situation
> where only one device is served until all bios are submitted, and only
> then the next device is served. This is obviously suboptimal.
> This patch just throws out the congestion detection and reschedules the
> worker every 8 requests. This way, all devices can be kept busy.
> This is only a temporary fix until the block layer provides a non-blocking
> submit_bio. Then the whole submit_worker mechanism can be killed.

Could you please try the top commit in for-linus instead?  It seems to
be helping here, although I wasn't able to trigger the same problems you
reported.

-chris
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