Re: [PATCH] blk: optimization for classic polling
On Tue, Feb 20, 2018 at 12:37:07PM -1000, Jens Axboe wrote: > On 2/20/18 3:21 AM, Peter Zijlstra wrote: > > On Sun, May 30, 2083 at 09:51:06AM +0530, Nitesh Shetty wrote: > >> This removes the dependency on interrupts to wake up task. Set task > >> state as TASK_RUNNING, if need_resched() returns true, > >> while polling for IO completion. > >> Earlier, polling task used to sleep, relying on interrupt to wake it up. > >> This made some IO take very long when interrupt-coalescing is enabled in > >> NVMe. > > > > This is a horrible Changelog.. it does not in fact explain why the patch > > works or is correct. > > Yeah, that should have been improved. Being ever more forgetful (I blame the kids) I find Changelogs more and more important, ymmv ;-) > > Also, set_current_state(TASK_RUNNING) is dodgy (similarly in > > __blk_mq_poll), why do you need that memory barrier? > > I pointed that out in the review, and v2 fixed it. v2 is the > one that got merged. Right missed that. In fact, possibly the only reason I saw this is that Nitesh had this computer configured wrong and the email is from the future and thus the very first entry in my lkml folder.
Re: [PATCH] blk: optimization for classic polling
On 2/20/18 3:21 AM, Peter Zijlstra wrote: > On Sun, May 30, 2083 at 09:51:06AM +0530, Nitesh Shetty wrote: >> This removes the dependency on interrupts to wake up task. Set task >> state as TASK_RUNNING, if need_resched() returns true, >> while polling for IO completion. >> Earlier, polling task used to sleep, relying on interrupt to wake it up. >> This made some IO take very long when interrupt-coalescing is enabled in >> NVMe. > > This is a horrible Changelog.. it does not in fact explain why the patch > works or is correct. Yeah, that should have been improved. > Also, set_current_state(TASK_RUNNING) is dodgy (similarly in > __blk_mq_poll), why do you need that memory barrier? I pointed that out in the review, and v2 fixed it. v2 is the one that got merged. -- Jens Axboe
Re: [PATCH] blk: optimization for classic polling
On Tue, Feb 20, 2018 at 02:21:37PM +0100, Peter Zijlstra wrote: > Also, set_current_state(TASK_RUNNING) is dodgy (similarly in > __blk_mq_poll), why do you need that memory barrier? You're right. The subsequent revision that was committed removed the barrier. The commit is here: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit?id=67b4110f8c8d16e588d7730db8e8b01b32c1bd8b I hope the code at least looks more reasonable. The changelog isn't much different, though.
Re: [PATCH] blk: optimization for classic polling
On Sun, May 30, 2083 at 09:51:06AM +0530, Nitesh Shetty wrote:
> This removes the dependency on interrupts to wake up task. Set task
> state as TASK_RUNNING, if need_resched() returns true,
> while polling for IO completion.
> Earlier, polling task used to sleep, relying on interrupt to wake it up.
> This made some IO take very long when interrupt-coalescing is enabled in
> NVMe.
This is a horrible Changelog.. it does not in fact explain why the patch
works or is correct.
Also, set_current_state(TASK_RUNNING) is dodgy (similarly in
__blk_mq_poll), why do you need that memory barrier?
> Signed-off-by: Nitesh Shetty
> ---
> fs/block_dev.c | 16
> fs/direct-io.c | 8 ++--
> fs/iomap.c | 10 +++---
> 3 files changed, 25 insertions(+), 9 deletions(-)
>
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 4a181fc..a87d8b7 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -236,9 +236,13 @@ __blkdev_direct_IO_simple(struct kiocb *iocb, struct
> iov_iter *iter,
> set_current_state(TASK_UNINTERRUPTIBLE);
> if (!READ_ONCE(bio.bi_private))
> break;
> - if (!(iocb->ki_flags & IOCB_HIPRI) ||
> - !blk_poll(bdev_get_queue(bdev), qc))
> + if (!(iocb->ki_flags & IOCB_HIPRI))
> io_schedule();
> + else if (!blk_poll(bdev_get_queue(bdev), qc)) {
> + if (need_resched())
> + set_current_state(TASK_RUNNING);
> + io_schedule();
> + }
> }
> __set_current_state(TASK_RUNNING);
>
Re: [PATCH] blk: optimization for classic polling
On 05/29/83 20:21, Nitesh Shetty wrote: [ ... ] Hello Nitesh, Can you check the clock of the system you used to send this e-mail? In the header of your e-mail I found the following: Date: Sun, 30 May 2083 09:51:06 +0530 Thanks, Bart.
Re: [PATCH] blk: optimization for classic polling
I think it'd be simpler to have blk_poll set it back to running if need_resched is true rather than repeat this patter across all the callers: --- diff --git a/block/blk-mq.c b/block/blk-mq.c index df93102e2149..40285fe1c8ad 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -3164,6 +3164,7 @@ static bool __blk_mq_poll(struct blk_mq_hw_ctx *hctx, struct request *rq) cpu_relax(); } + set_current_state(TASK_RUNNING); return false; } -- Nice!
Re: [PATCH] blk: optimization for classic polling
On Sun, May 30, 2083 at 09:51:06AM +0530, Nitesh Shetty wrote: > This removes the dependency on interrupts to wake up task. Set task > state as TASK_RUNNING, if need_resched() returns true, > while polling for IO completion. > Earlier, polling task used to sleep, relying on interrupt to wake it up. > This made some IO take very long when interrupt-coalescing is enabled in > NVMe. > > Reference: > http://lists.infradead.org/pipermail/linux-nvme/2018-February/015435.html > Signed-off-by: Nitesh Shetty > --- > fs/block_dev.c | 16 > fs/direct-io.c | 8 ++-- > fs/iomap.c | 10 +++--- > 3 files changed, 25 insertions(+), 9 deletions(-) I think it'd be simpler to have blk_poll set it back to running if need_resched is true rather than repeat this patter across all the callers: --- diff --git a/block/blk-mq.c b/block/blk-mq.c index df93102e2149..40285fe1c8ad 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -3164,6 +3164,7 @@ static bool __blk_mq_poll(struct blk_mq_hw_ctx *hctx, struct request *rq) cpu_relax(); } + set_current_state(TASK_RUNNING); return false; } --
