On 2/16/23 08:40, Keith Busch wrote: > On Thu, Feb 16, 2023 at 12:50:03PM +0100, Hannes Reinecke wrote: >> Hi all, >> >> it has come up in other threads, so it might be worthwhile to have its own >> topic: >> >> Userspace command aborts >> >> As it stands we cannot abort I/O commands from userspace. >> This is hitting us when running in a virtual machine: >> The VM sets a timeout when submitting a command, but that >> information can't be transmitted to the VM host. The VM host >> then issues a different command (with another timeout), and >> again that timeout can't be transmitted to the attached devices. >> So when the VM detects a timeout, it will try to issue an abort, >> but that goes nowhere as the VM host has no way to abort commands >> from userspace. >> So in the end the VM has to wait for the command to complete, causing >> stalls in the VM if the host had to undergo error recovery or something. > > Aborts are racy. A lot of hardware implements these as a no-op, too. > I'd avoid implementing userspace aborts and fix things in spec first. -ck
