Fengnan Chang <changfengnan@xxxxxxxxxxxxx> writes: > Christoph Hellwig <hch@xxxxxxxxxxxxx> 于2025年8月25日周一 17:21写道： >> >> On Mon, Aug 25, 2025 at 04:51:27PM +0800, Fengnan Chang wrote: >> > No restrictions for now, I think we can enable this by default. >> > Maybe better solution is modify in bio.c? Let me do some test first. If there are other implications to consider, for using per-cpu bio cache by default, then maybe we can first get the optimizations for iomap in for at least REQ_ALLOC_CACHE users and later work on to see if this can be enabled by default for other users too. Unless someone else thinks otherwise. Why I am thinking this is - due to limited per-cpu bio cache if everyone uses it for their bio submission, we may not get the best performance where needed. So that might require us to come up with a different approach. >> >> Any kind of numbers you see where this makes a different, including >> the workloads would also be very valuable here. > I'm test random direct read performance on io_uring+ext4, and try > compare to io_uring+ raw blkdev, io_uring+ext4 is quite poor, I'm try to > improve this, I found ext4 is quite different with blkdev when run > bio_alloc_bioset. It's beacuse blkdev ext4 use percpu bio cache, but ext4 > path not. So I make this modify. I am assuming you meant to say - DIO with iouring+raw_blkdev uses per-cpu bio cache where as iouring+(ext4/xfs) does not use it. Hence you added this patch which will enable the use of it - which should also improve the performance of iouring+(ext4/xfs). That make sense to me. > My test command is: > /fio/t/io_uring -p0 -d128 -b4096 -s1 -c1 -F1 -B1 -R1 -X1 -n1 -P1 -t0 > /data01/testfile > Without this patch: > BW is 1950MB > with this patch > BW is 2001MB. Ok. That's around 2.6% improvement.. Is that what you were expecting to see too? Is that because you were testing with -p0 (non-polled I/O)? Looking at the numbers here [1] & [2], I was hoping this could give maybe around 5-6% improvement ;) [1]: https://lore.kernel.org/io-uring/cover.1666347703.git.asml.silence@xxxxxxxxx/ [2]: https://lore.kernel.org/all/20220806152004.382170-3-axboe@xxxxxxxxx/ -ritesh
