Hi Chris, On 07/12/2018 01:45 AM, Chris wrote: > On Wed, Jul 11, 2018 at 12:43 PM, Greg Kurz <gr...@kaod.org> wrote: >> I've been observing a similar delay on ppc64 with fedora28 guests: >> >> # dmesg | egrep 'scsi| sd ' >> [ 1.530946] scsi host0: Virtio SCSI HBA >> [ 1.532452] scsi 0:0:0:0: Direct-Access QEMU QEMU HARDDISK >> 2.5+ PQ: 0 ANSI: 5 >> [ 21.928378] sd 0:0:0:0: Power-on or device reset occurred >> [ 21.930012] sd 0:0:0:0: Attached scsi generic sg0 type 0 >> [ 21.931554] sd 0:0:0:0: [sda] 83886080 512-byte logical blocks: (42.9 >> GB/40.0 GiB) >> [ 21.931929] sd 0:0:0:0: [sda] Write Protect is off >> [ 21.933110] sd 0:0:0:0: [sda] Mode Sense: 63 00 00 08 >> [ 21.934084] sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, >> doesn't support DPO or FUA >> [ 21.943566] sd 0:0:0:0: [sda] Attached SCSI disk >> >> Kernel version is 4.16.16-300.fc28.ppc64. And I cannot reproduce the >> issue with other distros that have an older kernel, eg, ubuntu 18.04 >> with kernel 4.15.0-23-generic. >> >> My first guess is that it might be a kernel-side regression introduced >> in 4.16... maybe bisect ? > > Interesting. I just tried kernel 4.17.5 from the mainline ppa on > Ubuntu 18.04 and now there is a delay. It's only 7.5 seconds but still > noticeable. There was previously no delay with the 4.15 kernel.
I did not observe any delay with stable 4.17.5 on ubuntu 18.04 (I built the kernel myself with CONFIG_SCSI_VIRTIO=y): # qemu-system-x86_64 -drive file=/home/zhang/img/ubuntu1804.qcow2,format=qcow2,if=none,id=virt1 -device virtio-scsi-pci,id=virt1 -device scsi-hd,drive=virt1 -m 4096M -enable-kvm -smp 6 -net nic -net user,hostfwd=tcp::5022-:22 -kernel /home/zhang/test/linux-4.17.5/arch/x86_64/boot/bzImage -append "root=/dev/sda1 init=/sbin/init text" -enable-kvm # uname -r 4.17.5 [0.190434] scsi host0: Virtio SCSI HBA [0.190924] scsi 0:0:0:0: Direct-Access QEMU QEMU HARDDISK 2.5+ PQ: 0 ANSI: 5 [0.206282] random: fast init done [0.216651] sd 0:0:0:0: Power-on or device reset occurred [0.216907] sd 0:0:0:0: Attached scsi generic sg0 type 0 [0.217207] ata_piix 0000:00:01.1: version 2.13 [0.217613] sd 0:0:0:0: [sda] 62914560 512-byte logical blocks: (32.2 GB/30.0 GiB) [0.217959] sd 0:0:0:0: [sda] Write Protect is off [0.218152] sd 0:0:0:0: [sda] Mode Sense: 63 00 00 08 [0.218193] sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA In addition, I could not reproduce with '4.18-rc4' or 'v4.17-rc7'. Dongli Zhang > > Definitely seems like it could be something introduced in kernel 4.16. > > Chris >
