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Tue, 01 Jul 2025 15:11:38 -0700 (PDT) Message-ID: <90fa0bd9-71b7-44f7-9175-641d43e9fe1b@kernel.dk> Date: Tue, 1 Jul 2025 16:11:37 -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: Weird delay introduced in v6.16-rc only, possible regression To: Qu Wenruo , "linux-block@vger.kernel.org" , LKML References: <20f07b3b-194a-4dfe-936e-0f159bf44485@kernel.dk> <69ea6e7a-a6f9-4199-9dc4-01b37092795f@gmx.com> From: Jens Axboe Content-Language: en-US In-Reply-To: <69ea6e7a-a6f9-4199-9dc4-01b37092795f@gmx.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/1/25 4:07 PM, Qu Wenruo wrote: > > > ? 2025/7/2 02:00, Jens Axboe ??: >> On 6/29/25 3:45 PM, Qu Wenruo wrote: >>> Hi, >>> >>> Recently I'm hitting a very weird delay when doing development inside a x86_64 VM. >>> >>> The dmesg shows the delay (10+ sec) between virtio blk and device-mapper: >>> >>> [ 3.651377] virtio_blk virtio4: 10/0/0 default/read/poll queues >>> [ 3.653075] virtio_scsi virtio2: 10/0/0 default/read/poll queues >>> [ 3.670269] virtio_blk virtio4: [vda] 83886080 512-byte logical blocks (42.9 GB/40.0 GiB) >>> [ 3.672096] scsi host6: Virtio SCSI HBA >>> [ 3.708452] vda: vda1 vda2 >>> [ 3.711073] virtio_blk virtio5: 10/0/0 default/read/poll queues >>> [ 3.729879] virtio_blk virtio5: [vdb] 167772160 512-byte logical blocks (85.9 GB/80.0 GiB) >>> [ 3.737535] virtio_blk virtio8: 10/0/0 default/read/poll queues >>> [ 3.747045] virtio_blk virtio8: [vdc] 83886080 512-byte logical blocks (42.9 GB/40.0 GiB) >>> [ 17.453833] device-mapper: uevent: version 1.0.3 >>> [ 17.455689] device-mapper: ioctl: 4.50.0-ioctl (2025-04-28) initialised: dm-devel@lists.linux.dev >>> :: performing fsck on '/dev/os/root' >>> /dev/mapper/os-root: clean, 240299/1048576 files, 3372218/4194304 blocks >>> :: mounting '/dev/os/root' on real root >>> [ 17.871671] EXT4-fs (dm-0): mounted filesystem 00a85626-d289-4817-8183-ee828e221f76 r/w with ordered data mode. Quota mode: none. >>> >>> The VM is running kernel based on upstream commit 78f4e737a53e ("Merge tag 'for-6.16/dm-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm"), with a lot of extra btrfs patches. >>> >>> >>> The v6.15 kernel from Archlinux is totally fine without any delay. >>> >>> The v6.16-rc kernel may have some different configs, but the config is used for a long long time, way before v6.15, so it looks like it's something in the v6.16 cycle causing problems. >>> >>> I can definitely do a bisection, but any clue would be appreciated. >> >> Probably a good idea to go ahead with a bisect to help pin it down. >> > > BTW, a little more digging shows it's the `udevadm settle` causing the long delay in the initramfs. > > The rootfs is an ext4 on a LVM lv, so initramfs is required to mount the rootfs. > > So it may not be the block/dm layer causing the problem. Even the more reason to bisect it then, if we don't quite know why it's slow. -- Jens Axboe