[dm-devel] [PATCH V3 0/5] dm-rq: improve sequential I/O performance

[Bart Van Assche]

On Fri, 2018-01-12 at 19:52 -0500, Mike Snitzer wrote:
> It was 50 ms before it was 100 ms.  No real explaination for these
> values other than they seem to make Bart's IB SRP testbed happy?

But that constant was not introduced by me in the dm code. See e.g. the
following commits:

commit d548b34b062b60b4f4df295a0b4823dfda1f1fc4
Author: Mike Snitzer <snitzer at redhat.com>
Date:   Thu Mar 5 22:21:10 2015 -0500

    dm: reduce the queue delay used in dm_request_fn from 100ms to 10ms
     
    Commit 7eaceaccab ("block: remove per-queue plugging") didn't justify
    DM's use of a 100ms delay; such an extended delay is a liability when
    there is reason to re-kick the queue.
     
    Signed-off-by: Mike Snitzer <snitzer at redhat.com>

commit 7eaceaccab5f40bbfda044629a6298616aeaed50
Author: Jens Axboe <jaxboe at fusionio.com>
Date:   Thu Mar 10 08:52:07 2011 +0100

    block: remove per-queue plugging
     
    Code has been converted over to the new explicit on-stack plugging,
    and delay users have been converted to use the new API for that.
    So lets kill off the old plugging along with aops->sync_page().
     
    Signed-off-by: Jens Axboe <jaxboe at fusionio.com>

Bart.