| Message ID | 20230718194920.1472184-7-axboe@kernel.dk (mailing list archive) |
|---|---|
| State | Superseded, archived |
| Headers | show |
| Series | Improve async iomap DIO performance | expand |
On Tue, Jul 18, 2023 at 01:49:20PM -0600, Jens Axboe wrote: > If IOCB_DIO_DEFER is set, utilize that to set kiocb->dio_complete handler > and data for that callback. Rather than punt the completion to a > workqueue, we pass back the handler and data to the issuer and will get a > callback from a safe task context. > > Using the following fio job to randomly dio write 4k blocks at > queue depths of 1..16: > > fio --name=dio-write --filename=/data1/file --time_based=1 \ > --runtime=10 --bs=4096 --rw=randwrite --norandommap --buffered=0 \ > --cpus_allowed=4 --ioengine=io_uring --iodepth=16 > > shows the following results before and after this patch: > > Stock Patched Diff > ======================================= > QD1 155K 162K + 4.5% > QD2 290K 313K + 7.9% > QD4 533K 597K +12.0% > QD8 604K 827K +36.9% > QD16 615K 845K +37.4% Nice. > which shows nice wins all around. If we factored in per-IOP efficiency, > the wins look even nicer. This becomes apparent as queue depth rises, > as the offloaded workqueue completions runs out of steam. > > Signed-off-by: Jens Axboe <axboe@kernel.dk> > --- > fs/iomap/direct-io.c | 24 ++++++++++++++++++++++++ > 1 file changed, 24 insertions(+) > > diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c > index 92b9b9db8b67..ed615177e1f6 100644 > --- a/fs/iomap/direct-io.c > +++ b/fs/iomap/direct-io.c > @@ -131,6 +131,11 @@ ssize_t iomap_dio_complete(struct iomap_dio *dio) > } > EXPORT_SYMBOL_GPL(iomap_dio_complete); > > +static ssize_t iomap_dio_deferred_complete(void *data) > +{ > + return iomap_dio_complete(data); > +} > + > static void iomap_dio_complete_work(struct work_struct *work) > { > struct iomap_dio *dio = container_of(work, struct iomap_dio, aio.work); > @@ -167,6 +172,25 @@ void iomap_dio_bio_end_io(struct bio *bio) > } else if ((dio->flags & IOMAP_DIO_INLINE_COMP) && in_task()) { > WRITE_ONCE(dio->iocb->private, NULL); > iomap_dio_complete_work(&dio->aio.work); > + } else if ((dio->flags & IOMAP_DIO_INLINE_COMP) && > + (iocb->ki_flags & IOCB_DIO_DEFER)) { > + /* only polled IO cares about private cleared */ > + iocb->private = dio; > + iocb->dio_complete = iomap_dio_deferred_complete; > + /* > + * Invoke ->ki_complete() directly. We've assigned > + * out dio_complete callback handler, and since the > + * issuer set IOCB_DIO_DEFER, we know their > + * ki_complete handler will notice ->dio_complete > + * being set and will defer calling that handler > + * until it can be done from a safe task context. > + * > + * Note that the 'res' being passed in here is > + * not important for this case. The actual completion > + * value of the request will be gotten from dio_complete > + * when that is run by the issuer. > + */ > + iocb->ki_complete(iocb, 0); > } else { > struct inode *inode = file_inode(iocb->ki_filp); > Hmmm. No problems with the change, but all the special cases is making the completion function a bit of a mess. Given that all read DIOs use inline completions, we can largely simplify the completion down to just looking at dio->wait_for_completion and IOMAP_DIO_COMPLETE_INLINE, and not caring about what type of IO is being completed at all. Hence I think that at the end of this series, the completion function should look something like this: void iomap_dio_bio_end_io(struct bio *bio) { struct iomap_dio *dio = bio->bi_private; struct kiocb *iocb = dio->iocb; bool should_dirty = (dio->flags & IOMAP_DIO_DIRTY); ssize_t result = 0; if (bio->bi_status) iomap_dio_set_error(dio, blk_status_to_errno(bio->bi_status)); if (!atomic_dec_and_test(&dio->ref)) goto release_bio; /* Synchronous IO completion. */ if (dio->wait_for_completion) { struct task_struct *waiter = dio->submit.waiter; WRITE_ONCE(dio->submit.waiter, NULL); blk_wake_io_task(waiter); goto release_bio; } /* * Async DIO completion that requires filesystem level * completion work gets punted to a work queue to complete * as the operation may require more IO to be issued to * finalise filesystem metadata changes or guarantee data * integrity. */ if (!(dio->flags & IOMAP_DIO_COMPLETE_INLINE)) { struct inode *inode = file_inode(iocb->ki_filp); WRITE_ONCE(iocb->private, NULL); INIT_WORK(&dio->aio.work, iomap_dio_complete_work); queue_work(inode->i_sb->s_dio_done_wq, &dio->aio.work); goto release_bio; } /* * Inline completion for async DIO. * * If the IO submitter is running DIO completions directly * itself, set up the callback it needs. The value we pass * to .ki_complete in this case does not matter, the defered * completion will pull the result from the completion * callback we provide. * * Otherwise, run the dio completion directly, then pass the * result to the iocb completion function to finish the IO. */ if (iocb->ki_flags & IOCB_DEFER_DIO) { WRITE_ONCE(iocb->private, dio); iocb->dio_complete = iomap_dio_deferred_complete; } else { WRITE_ONCE(dio->iocb->private, NULL); result = iomap_dio_complete(dio); } iocb->ki_complete(iocb, result); release_bio: if (should_dirty) { bio_check_pages_dirty(bio); } else { bio_release_pages(bio, false); bio_put(bio); } } -Dave.
On 7/18/23 5:50?PM, Dave Chinner wrote: >> @@ -167,6 +172,25 @@ void iomap_dio_bio_end_io(struct bio *bio) >> } else if ((dio->flags & IOMAP_DIO_INLINE_COMP) && in_task()) { >> WRITE_ONCE(dio->iocb->private, NULL); >> iomap_dio_complete_work(&dio->aio.work); >> + } else if ((dio->flags & IOMAP_DIO_INLINE_COMP) && >> + (iocb->ki_flags & IOCB_DIO_DEFER)) { >> + /* only polled IO cares about private cleared */ >> + iocb->private = dio; >> + iocb->dio_complete = iomap_dio_deferred_complete; >> + /* >> + * Invoke ->ki_complete() directly. We've assigned >> + * out dio_complete callback handler, and since the >> + * issuer set IOCB_DIO_DEFER, we know their >> + * ki_complete handler will notice ->dio_complete >> + * being set and will defer calling that handler >> + * until it can be done from a safe task context. >> + * >> + * Note that the 'res' being passed in here is >> + * not important for this case. The actual completion >> + * value of the request will be gotten from dio_complete >> + * when that is run by the issuer. >> + */ >> + iocb->ki_complete(iocb, 0); >> } else { >> struct inode *inode = file_inode(iocb->ki_filp); >> > > Hmmm. No problems with the change, but all the special cases is > making the completion function a bit of a mess. > > Given that all read DIOs use inline completions, we can largely > simplify the completion down to just looking at > dio->wait_for_completion and IOMAP_DIO_COMPLETE_INLINE, and not > caring about what type of IO is being completed at all. > > Hence I think that at the end of this series, the completion > function should look something like this: I took inspiration from this as I think it's a good idea, and did a few cleanups and introduced things like the above as we go. It's in v3 I just posted.
diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c index 92b9b9db8b67..ed615177e1f6 100644 --- a/fs/iomap/direct-io.c +++ b/fs/iomap/direct-io.c @@ -131,6 +131,11 @@ ssize_t iomap_dio_complete(struct iomap_dio *dio) } EXPORT_SYMBOL_GPL(iomap_dio_complete); +static ssize_t iomap_dio_deferred_complete(void *data) +{ + return iomap_dio_complete(data); +} + static void iomap_dio_complete_work(struct work_struct *work) { struct iomap_dio *dio = container_of(work, struct iomap_dio, aio.work); @@ -167,6 +172,25 @@ void iomap_dio_bio_end_io(struct bio *bio) } else if ((dio->flags & IOMAP_DIO_INLINE_COMP) && in_task()) { WRITE_ONCE(dio->iocb->private, NULL); iomap_dio_complete_work(&dio->aio.work); + } else if ((dio->flags & IOMAP_DIO_INLINE_COMP) && + (iocb->ki_flags & IOCB_DIO_DEFER)) { + /* only polled IO cares about private cleared */ + iocb->private = dio; + iocb->dio_complete = iomap_dio_deferred_complete; + /* + * Invoke ->ki_complete() directly. We've assigned + * out dio_complete callback handler, and since the + * issuer set IOCB_DIO_DEFER, we know their + * ki_complete handler will notice ->dio_complete + * being set and will defer calling that handler + * until it can be done from a safe task context. + * + * Note that the 'res' being passed in here is + * not important for this case. The actual completion + * value of the request will be gotten from dio_complete + * when that is run by the issuer. + */ + iocb->ki_complete(iocb, 0); } else { struct inode *inode = file_inode(iocb->ki_filp);
If IOCB_DIO_DEFER is set, utilize that to set kiocb->dio_complete handler and data for that callback. Rather than punt the completion to a workqueue, we pass back the handler and data to the issuer and will get a callback from a safe task context. Using the following fio job to randomly dio write 4k blocks at queue depths of 1..16: fio --name=dio-write --filename=/data1/file --time_based=1 \ --runtime=10 --bs=4096 --rw=randwrite --norandommap --buffered=0 \ --cpus_allowed=4 --ioengine=io_uring --iodepth=16 shows the following results before and after this patch: Stock Patched Diff ======================================= QD1 155K 162K + 4.5% QD2 290K 313K + 7.9% QD4 533K 597K +12.0% QD8 604K 827K +36.9% QD16 615K 845K +37.4% which shows nice wins all around. If we factored in per-IOP efficiency, the wins look even nicer. This becomes apparent as queue depth rises, as the offloaded workqueue completions runs out of steam. Signed-off-by: Jens Axboe <axboe@kernel.dk> --- fs/iomap/direct-io.c | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+)