From: Pavel Begunkov <asml.silence@gmail.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: linux-block@vger.kernel.org, Jens Axboe <axboe@kernel.dk>
Subject: Re: [PATCH 3/5] block: avoid extra iter advance with async iocb
Date: Mon, 25 Oct 2021 12:10:14 +0100 [thread overview]
Message-ID: <87d9f109-c00e-7e79-36c3-61f153db3561@gmail.com> (raw)
In-Reply-To: <YXZd3ETk4P+OBWXD@infradead.org>
On 10/25/21 08:33, Christoph Hellwig wrote:
> On Sat, Oct 23, 2021 at 05:21:34PM +0100, Pavel Begunkov wrote:
>> --- a/block/fops.c
>> +++ b/block/fops.c
>> @@ -352,11 +352,21 @@ static ssize_t __blkdev_direct_IO_async(struct kiocb *iocb,
>> bio->bi_end_io = blkdev_bio_end_io_async;
>> bio->bi_ioprio = iocb->ki_ioprio;
>>
>> - ret = bio_iov_iter_get_pages(bio, iter);
>> - if (unlikely(ret)) {
>> - bio->bi_status = BLK_STS_IOERR;
>> - bio_endio(bio);
>> - return ret;
>> + if (!iov_iter_is_bvec(iter)) {
>> + ret = bio_iov_iter_get_pages(bio, iter);
>> + if (unlikely(ret)) {
>> + bio->bi_status = BLK_STS_IOERR;
>> + bio_endio(bio);
>> + return ret;
>> + }
>
> Nit: I generally find it much nicer to read if simple if statements
> don't use pointless negations.
>
>> + } else {
>> + /*
>> + * Users don't rely on the iterator being in any particular
>> + * state for async I/O returning -EIOCBQUEUED, hence we can
>> + * avoid expensive iov_iter_advance(). Bypass
>> + * bio_iov_iter_get_pages() and set the bvec directly.
>> + */
>> + bio_iov_bvec_set(bio, iter);
>
> So if this optimization is so useful, please also do it for
> non-bvec iov_iters, which is what 99% of the applications actually
> use.
It's an async path, so mainly io_uring or aio, I don't think there
is much profit in doing that for iov, especially behind iov -> bvec
translation with page referencing.
Could've been done nonetheless, but what I think about looks too
ugly because of the loop inside of bio_iov_iter_get_pages(). Don't
think the sketch below is viable, any better ideas?
ssize_t __bio_iov_iter_get_pages() {
...
/* not advancing */
return size;
}
do {
if (bio_op(bio) == REQ_OP_ZONE_APPEND)
ret = __bio_iov_append_get_pages(bio, iter);
else
ret = __bio_iov_iter_get_pages(bio, iter);
if (ret < 0)
break;
iov_iter_advance(ret);
} while (iov_iter_count(iter) && !bio_full(bio, 0));
and copy paste into fops.c
do {
if (bio_op(bio) == REQ_OP_ZONE_APPEND)
ret = __bio_iov_append_get_pages(bio, iter);
else
ret = __bio_iov_iter_get_pages(bio, iter);
if (ret < 0 || iov_iter_count(iter) == ret || bio_full(bio, 0))
break;
iov_iter_advance(ret);
} while (1);
--
Pavel Begunkov
next prev parent reply other threads:[~2021-10-25 11:12 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-23 16:21 [PATCH 0/5] block optimisations Pavel Begunkov
2021-10-23 16:21 ` [PATCH 1/5] block: add single bio async direct IO helper Pavel Begunkov
2021-10-23 16:21 ` [PATCH 2/5] block: refactor bio_iov_bvec_set() Pavel Begunkov
2021-10-25 7:31 ` Christoph Hellwig
2021-10-23 16:21 ` [PATCH 3/5] block: avoid extra iter advance with async iocb Pavel Begunkov
2021-10-25 7:33 ` Christoph Hellwig
2021-10-25 11:10 ` Pavel Begunkov [this message]
2021-10-23 16:21 ` [PATCH 4/5] block: kill unused polling bits in __blkdev_direct_IO() Pavel Begunkov
2021-10-23 16:46 ` Pavel Begunkov
2021-10-24 15:09 ` Jens Axboe
2021-10-24 17:17 ` Pavel Begunkov
2021-10-24 18:11 ` Jens Axboe
2021-10-25 7:35 ` Christoph Hellwig
2021-10-25 10:12 ` Pavel Begunkov
2021-10-25 10:27 ` Pavel Begunkov
2021-10-27 6:47 ` Christoph Hellwig
2021-10-23 16:21 ` [PATCH 5/5] block: add async version of bio_set_polled Pavel Begunkov
2021-10-25 7:36 ` Christoph Hellwig
2021-10-25 10:20 ` Pavel Begunkov
2021-10-25 7:28 ` [PATCH 0/5] block optimisations Christoph Hellwig
2021-10-26 23:30 ` (subset) " Jens Axboe
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