Re: [PATCH V5 0/6] blk-mq: support batching dispatch from scheduler

[Ming Lei <ming.lei@redhat.com>]

On Wed, Jun 24, 2020 at 02:17:28PM -0700, Sagi Grimberg wrote:
> 
> > Hi Jens,
> > 
> > More and more drivers want to get batching requests queued from
> > block layer, such as mmc[1], and tcp based storage drivers[2]. Also
> > current in-tree users have virtio-scsi, virtio-blk and nvme.
> > 
> > For none, we already support batching dispatch.
> > 
> > But for io scheduler, every time we just take one request from scheduler
> > and pass the single request to blk_mq_dispatch_rq_list(). This way makes
> > batching dispatch not possible when io scheduler is applied. One reason
> > is that we don't want to hurt sequential IO performance, becasue IO
> > merge chance is reduced if more requests are dequeued from scheduler
> > queue.
> > 
> > Tries to start the support by dequeuing more requests from scheduler
> > if budget is enough and device isn't busy.
> > 
> > Simple fio test over virtio-scsi shows IO can get improved by 5~10%.
> > 
> > Baolin has tested previous versions and found performance on MMC can be improved.
> > 
> > Patch 1 ~ 4 are improvement and cleanup, which can't applied without
> > supporting batching dispatch.
> > 
> > Patch 5 ~ 6 starts to support batching dispatch from scheduler.
> > 
> > 
> > 
> > [1] https://lore.kernel.org/linux-block/20200512075501.GF1531898@T590/#r
> > [2] https://lore.kernel.org/linux-block/fe6bd8b9-6ed9-b225-f80c-314746133722@grimberg.me/
> > 
> > V5:
> > 	- code style changes suggested by Damien
> > 
> > V4:
> > 	- fix releasing budgets and avoids IO hang(5/6)
> > 	- dispatch more batches if the device can accept more(6/6)
> > 	- verified by running more tests
> > 
> > V3:
> > 	- add reviewed-by tag
> > 	- fix one typo
> > 	- fix one budget leak issue in case that .queue_rq returned *_RESOURCE in 5/6
> > 
> > V2:
> > 	- remove 'got_budget' from blk_mq_dispatch_rq_list
> > 	- drop patch for getting driver tag & handling partial dispatch
> 
> Hey Ming,
> 
> What ever happened to this one?

Hi Sagi,

Looks the 1st patch can't be applied cleanly against for-5.9/block, I will send
V6 later.

thanks,
Ming