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Wed, 16 Apr 2025 08:07:17 -0700 (PDT) Message-ID: <37c982b5-92e1-4253-b8ac-d446a9a7d932@kernel.dk> Date: Wed, 16 Apr 2025 09:07:17 -0600 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] io_uring/rsrc: send exact nr_segs for fixed buffer To: Pavel Begunkov , Nitesh Shetty Cc: gost.dev@samsung.com, nitheshshetty@gmail.com, io-uring@vger.kernel.org, linux-kernel@vger.kernel.org References: <20250416054413.10431-1-nj.shetty@samsung.com> <98f08b07-c8de-4489-9686-241c0aab6acc@gmail.com> Content-Language: en-US From: Jens Axboe In-Reply-To: <98f08b07-c8de-4489-9686-241c0aab6acc@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 4/16/25 9:03 AM, Pavel Begunkov wrote: > On 4/16/25 06:44, Nitesh Shetty wrote: >> 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 >> --- >> io_uring/rsrc.c | 3 +++ >> 1 file changed, 3 insertions(+) >> >> diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c >> index b36c8825550e..6fd3a4a85a9c 100644 >> --- a/io_uring/rsrc.c >> +++ b/io_uring/rsrc.c >> @@ -1096,6 +1096,9 @@ static int io_import_fixed(int ddir, struct iov_iter *iter, >> iter->iov_offset = offset & ((1UL << imu->folio_shift) - 1); >> } >> } >> + iter->nr_segs = (iter->bvec->bv_offset + iter->iov_offset + >> + iter->count + ((1UL << imu->folio_shift) - 1)) / >> + (1UL << imu->folio_shift); > > That's not going to work with ->is_kbuf as the segments are not uniform in > size. Oops yes good point. > And can we make it saner? Split it into several statements, add variables > for folio size and so, or maybe just use ALIGN. If moved above, you > probably don't even need to recalc > > iter->bvec->bv_offset + iter->iov_offset Agree, was trying to do that with the shift at least, but seems like there is indeed room for further improvements here in terms of readability. -- Jens Axboe