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Tsirkin" , Jason Wang , Paolo Bonzini , Stefan Hajnoczi , =?UTF-8?Q?Eugenio_P=C3=A9rez?= , Xuan Zhuo , Keith Busch , Christoph Hellwig , Sagi Grimberg , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux.dev, linux-nvme@lists.infradead.org, linux-fsdevel@vger.kernel.org References: <20250611121626.7252-1-abuehaze@amazon.com> From: Jens Axboe Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 6/11/25 9:10 AM, Ming Lei wrote: > On Wed, Jun 11, 2025 at 12:14:54PM +0000, Hazem Mohamed Abuelfotoh wrote: >> This reverts commit e70c301faece15b618e54b613b1fd6ece3dd05b4. >> >> Commit ("block: don't reorder requests in >> blk_add_rq_to_plug") reversed how requests are stored in the blk_plug >> list, this had significant impact on bio merging with requests exist on >> the plug list. This impact has been reported in [1] and could easily be >> reproducible using 4k randwrite fio benchmark on an NVME based SSD without >> having any filesystem on the disk. >> >> My benchmark is: >> >> fio --time_based --name=benchmark --size=50G --rw=randwrite \ >> --runtime=60 --filename="/dev/nvme1n1" --ioengine=psync \ >> --randrepeat=0 --iodepth=1 --fsync=64 --invalidate=1 \ >> --verify=0 --verify_fatal=0 --blocksize=4k --numjobs=4 \ >> --group_reporting >> >> On 1.9TiB SSD(180K Max IOPS) attached to i3.16xlarge AWS EC2 instance. >> >> Kernel | fio (B.W MiB/sec) | I/O size (iostat) >> --------------+---------------------+-------------------- >> 6.15.1 | 362 | 2KiB >> 6.15.1+revert | 660 (+82%) | 4KiB >> --------------+---------------------+-------------------- > > I just run one quick test in my test VM, but can't reproduce it. > > Also be curious, why does writeback produce so many 2KiB bios? I was pondering that too, sounds like a misconfiguration of sorts. But even without that, in a quick synthetic test here locally, I do see a lot of missed merges that is solved with the alternative patch I sent out. I strongly suspect it'll fix this issue too. -- Jens Axboe