On 02/13/2017 08:04 PM, Benjamin Herrenschmidt wrote: > On Mon, 2017-02-13 at 15:57 -0600, Brian King wrote: >> If we do transition to use remove rather than shutdown, I think we >> want >> some way for a device driver to know whether we are doing kexec or >> not. >> A RAID adapter with a write cache is going to want to flush its write >> cache on a PCI hotplug remove, but for a kexec, its going to want to >> skip >> that so the kexec is faster. Today, since kexec looks like a reboot, >> rather than a shutdown, we can skip the flush on a reboot, since its >> technically not needed there either. > > What happens if a non-flushed adapter gets a PERST ? It depends on the adapter, so it really needs to be a policy in the device driver. For any adapter that has a non volatile write cache, data must preserved, otherwise the write cache is not truly non volatile. For adapters with a volatile write cache, then its subject to the adapter hardware. For ipr adapters that have a volatile cache, they do guarantee the data is preserved across a PERST. > I wouldn't trust that 'don't have to flush' magic ... I really don't think we want to force RAID adapters that have gigabytes of *non volatile* write cache to flush their cache when we are merely performing a kexec. This can take several minutes in the worst case scenarios. -Brian -- Brian King Power Linux I/O IBM Linux Technology Center
