Re: [RFC 0/2] nocopy bvec for direct IO

[Jens Axboe]

On 12/8/20 7:19 PM, Pavel Begunkov wrote:
> The idea is to avoid copying, merging, etc. bvec from iterator to bio
> in direct I/O and use the one we've already got. Hook it up for io_uring.
> Had an eye on it for a long, and it also was brought up by Matthew
> just recently. Let me know if I forgot or misplaced some tags.
> 
> A benchmark got me 430KIOPS vs 540KIOPS, or +25% on bare metal. And perf
> shows that bio_iov_iter_get_pages() was taking ~20%. The test is pretty
> silly, but still imposing. I'll redo it closer to reality for next
> iteration, anyway need to double check some cases.
> 
> If same applied to iomap, common chunck can be moved from block_dev
> into bio_iov_iter_get_pages(), but if there any benefit for filesystems,
> they should explicitly opt in with ITER_BVEC_FLAG_FIXED.

Ran this on a real device, and I get a 10% bump in performance with it.
That's pretty amazing! So please do pursue this one and pull it to
completion.

-- 
Jens Axboe