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Wed, 16 Apr 2025 07:19:33 -0700 (PDT) Message-ID: <4ed32b40-47ee-43f8-b3e3-88fdc6ca60fa@kernel.dk> Date: Wed, 16 Apr 2025 08:19:33 -0600 Precedence: bulk X-Mailing-List: io-uring@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: Nitesh Shetty , Pavel Begunkov 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> Content-Language: en-US From: Jens Axboe In-Reply-To: <20250416054413.10431-1-nj.shetty@samsung.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 4/15/25 11:44 PM, 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 This must be a regression, do you know which block/io_uring side commit caused the splits to be done for fixed buffers? > 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); iter->nr_segs = (iter->bvec->bv_offset + iter->iov_offset + iter->count + ((1UL << imu->folio_shift) - 1)) >> imu->folio_shift; to avoid a division, seems worthwhile? -- Jens Axboe