On Mon, 1 July 2013 08:50:48 +0200, Hannes Reinecke wrote: > > This patchset implements a new 'eh_deadline' attribute to the > SCSI host. It will limit the overall SCSI EH runtime by a given > timeout. If the timeout is reached all intermediate EH steps > will be skipped and host reset will be scheduled immediately.
I have mixed opinions about the concept. Having a command timeout is of limited use if you can still spend several minutes after the timeout in random processing. Userspace either needs -EIO reasonably quickly after a command timeout or will have to implement it's own timeout mechanism. I prefer having a single implementation in the kernel, so your patches are a step in the right direction. Host reset is an expensive and harmful operation. You lose access to all devices behind the host. At best this is a performance blip, at worst someone actually cared about some realtime properties. My main grump is that a single bad device can trigger this behaviour, essentially doing a DoS on the rest of the system. While that problem is somewhat orthogonal, your patchset can only make matters worse. Ideally we would have a way to detect the system geometry and next the error location. If a single device is bad, don't ever do a host reset. If you have redundant paths, never do a host reset on both controllers at the same time. Etc, etc. Getting there will be a lot of work and the result may be too error-prone to maintain without constantly breaking one exotic setup or another. But if someone could pull it off, it would be really nice to have. That said, now I should actually read your patches. ;) Jörn -- Measure. Don't tune for speed until you've measured, and even then don't unless one part of the code overwhelms the rest. -- Rob Pike -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
