Re: [Xen-devel] blk_{get,put}_queue() use in blkback

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

It's really old code to let us keep a handle on the last request_queue we
stuffed a request onto. This is because we plug that queue until we have
finished pulling down a batch of blkfront work, then unplug it.

Is this the best way to do that? Is there a benefit to doing this in the
first place on 2.6 kernels? To be honest I do not know. We'd need to ask
someone like Jens Axboe, and/or just kill that code and measure resulting
disc throughput performance. My guess is that it's merely legacy cruft from
the 2.4 era of blkback (also I wrote that code back in 2004 and I remember
not having much of a clue at the time about Linux 2.4 block interfaces!).

 -- Keir

On 6/3/08 10:49, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:

> While these symbols are no longer available to modules in 2.6.25-rc4, it
> seems suspicious that blkback is the only user of them (outside of the
> block/ directory) even in 2.6.18 (and starting with 2.6.17, where all the
> other blk_put_queue() users were converted to blk_cleanup_queue(),
> which isn't what blkback wants; there were no other users of
> blk_get_queue() even in 2.6.5 - didn't check older code). Would it be
> possible for someone familiar with the block layer and blkback's
> interface to it to determine whether these calls aren't really left-overs?
> 
> Thanks, Jan
> 
> 
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