From 80c7378f94cf193cb3bd2101bbcd5aea78d0e211 Mon Sep 17 00:00:00 2001 From: Nitesh Shetty Date: Thu, 17 Apr 2025 10:32:34 +0100 Subject: [PATCH] io_uring/rsrc: send exact nr_segs for fixed buffer Sending exact nr_segs, avoids bio split check and processing in block layer, which takes around 5%[1] of overall CPU utilization. In our setup, we see overall improvement of IOPS from 7.15M to 7.65M [2] and 5% less CPU utilization. [1] 3.52% io_uring [kernel.kallsyms] [k] bio_split_rw_at 1.42% io_uring [kernel.kallsyms] [k] bio_split_rw 0.62% io_uring [kernel.kallsyms] [k] bio_submit_split [2] sudo taskset -c 0,1 ./t/io_uring -b512 -d128 -c32 -s32 -p1 -F1 -B1 -n2 -r4 /dev/nvme0n1 /dev/nvme1n1 Signed-off-by: Nitesh Shetty [Pavel: fixed for kbuf, rebased and reworked on top of cleanups] Signed-off-by: Pavel Begunkov Link: https://lore.kernel.org/r/7a1a49a8d053bd617c244291d63dbfbc07afde36.1744882081.git.asml.silence@gmail.com [axboe: fold in fix factoring in buf reg offset] Signed-off-by: Jens Axboe --- io_uring/rsrc.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c index 5cf854318b1dd..0c6d7e7415c8b 100644 --- a/io_uring/rsrc.c +++ b/io_uring/rsrc.c @@ -1037,6 +1037,7 @@ static int io_import_fixed(int ddir, struct iov_iter *iter, u64 buf_addr, size_t len) { const struct bio_vec *bvec; + size_t folio_mask; unsigned nr_segs; size_t offset; int ret; @@ -1067,6 +1068,7 @@ static int io_import_fixed(int ddir, struct iov_iter *iter, * 2) all bvecs are the same in size, except potentially the * first and last bvec */ + folio_mask = (1UL << imu->folio_shift) - 1; bvec = imu->bvec; if (offset >= bvec->bv_len) { unsigned long seg_skip; @@ -1075,10 +1077,9 @@ static int io_import_fixed(int ddir, struct iov_iter *iter, offset -= bvec->bv_len; seg_skip = 1 + (offset >> imu->folio_shift); bvec += seg_skip; - offset &= (1UL << imu->folio_shift) - 1; + offset &= folio_mask; } - - nr_segs = imu->nr_bvecs - (bvec - imu->bvec); + nr_segs = (offset + len + bvec->bv_offset + folio_mask) >> imu->folio_shift; iov_iter_bvec(iter, ddir, bvec, nr_segs, len); iter->iov_offset = offset; return 0; -- 2.39.5