linux-kernel - [PATCH BUGFIX 0/3] null_blk: fix throughout losses and hangs

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Date:	Mon,  2 Nov 2015 15:31:10 +0100
From:	Paolo Valente <paolo.valente@...more.it>
To:	Jens Axboe <axboe@...com>,
	Matias Bjørling <m@...rling.me>,
	Arianna Avanzini <avanzini@...gle.com>
Cc:	Paolo Valente <paolo.valente@...more.it>,
	Akinobu Mita <akinobu.mita@...il.com>,
	"Luis R. Rodriguez" <mcgrof@...e.com>,
	Ming Lei <ming.lei@...onical.com>,
	Mike Krinkin <krinkin.m.u@...il.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH BUGFIX 0/3] null_blk: fix throughout losses and hangs

Hi,
while doing some tests with the null_blk device driver, we bumped into
two problems: first, unjustified and in some cases high throughput
losses; second, actual hangs. These problems seem to be the
consequence of the combination of three causes, and this patchset
introduces a fix for each of these causes. In particular, changes
address:
. an apparent flaw in the logic with which delayed completions are
  implemented: this flaw causes, with unlucky but non-pathological
  workloads, actual request-completion delays to become arbitrarily
  larger than the configured delay;
. the missing restart of the device queue on the completion of a request in
  single-queue non-delayed mode;
. the overflow of the request-delay parameter, when extremely high values
  are used (e.g., to spot bugs).

To avoid possible confusion, we stress that these fixes *do not* have
anything to do with the problems highlighted in [1] (tests of the
multiqueue xen-blkfront and xen-blkback modules with null_blk).

You can find more details in the patch descriptions.

Thanks,
Paolo and Arianna

[1] https://lkml.org/lkml/2015/8/19/181

Arianna Avanzini (2):
  null_blk: guarantee device restart in all irq modes
  null_blk: change type of completion_nsec to unsigned long

Paolo Valente (1):
  null_blk: set a separate timer for each command

 drivers/block/null_blk.c | 94 +++++++++++++++++-------------------------------
 1 file changed, 33 insertions(+), 61 deletions(-)

-- 
1.9.1

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