On Fri, Jul 10, 2020 at 08:27:09PM +0300, Denis V. Lunev wrote: > There are severe delays with IO requests processing if QEMU is running in > virtual machine or over software defined storage. Such delays potentially > results in unpredictable guest behavior. For example, guests over IDE or > SATA drive could remount filesystem read-only if write is performed > longer than 10 seconds. > > Such reports are very complex to process. Some good starting point for this > seems quite reasonable. This patch provides one. It adds logging of such > potentially dangerous long IO operations. > > Signed-off-by: Denis V. Lunev <d...@openvz.org> > CC: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com> > CC: Kevin Wolf <kw...@redhat.com> > CC: Max Reitz <mre...@redhat.com>
If I understand correctly this only reports completed I/Os, so if the host hasn't given up on an I/O request yet then QEMU will not report it is taking a long time. In the meantime the guest could start printing timeout errors. I think this patch series is good as it is. In the future maybe a QMP command that lists in-flight I/O requests would be nice. That helps when troubleshooting I/Os that are hung. Stefan
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