On 8/24/23 07:43, chengming.zhou@xxxxxxxxx wrote:
From: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
The current queue_rqs() support has limitation that it can't work on
shared tags queue, which is resolved by patch 1-3. We move the account
of active requests to where we really allocate the driver tag.
This is clearer and matched with the unaccount side which now happen
when we put the driver tag. And we can remove RQF_MQ_INFLIGHT, which
was used to avoid double account problem of flush request.
Another problem is that the driver that support queue_rqs() has to
set inflight request table by itself, which is resolved in patch 4.
The patch 5 fixes a potential race problem which may cause false
timeout because of the reorder of rq->state and rq->deadline.
The patch 6 add support queue_rqs() for null_blk, which showed a
3.6% IOPS improvement in fio/t/io_uring benchmark on my test VM.
And we also use it for testing queue_rqs() on shared tags queue.
Hi Jens and Christoph,
This patch series would be simplified significantly if the code for
fair tag allocation would be removed first
(https://lore.kernel.org/linux-block/20230103195337.158625-1-bvanassche@xxxxxxx/,
January 2023).
It has been proposed to improve fair tag sharing but the complexity of
the proposed alternative is scary
(https://lore.kernel.org/linux-block/20230618160738.54385-1-yukuai1@xxxxxxxxxxxxxxx/,
June 2023).
Does everyone agree with removing the code for fair tag sharing - code
that significantly hurts performance of UFS devices and code that did
not exist in the legacy block layer?
Thanks,
Bart.
