Re: [Xen-devel] [PATCH] Add SCHEDOP_block_on

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 15 Mar 2006, at 23:58, Ryan wrote:

> I'm not 100% sure, but I believe that jiffies does not get updated 
> while
> interrupts are disabled (the timer is an interrupt in a domU, right?). 
> I
> could never verify from the source if this is the case, but if the pci
> backend disappears or stops responding while the pci frontend is 
> waiting
> for an operation to complete, this could be a problem for the new code
> in pcifront. I've been preparing my patch for late binding in the pci
> backend and if I unload the pci backend module (yes, unloading will 
> work
> with my patch!), the pci frontend domain appears to hang (inside of the
> while loop in do_pci_op()) whereas prior to the HYPERVISOR_poll call 
> and
> jiffies check, the ttl would count down to 0 and error out of the spin
> and clean-up gracefully. I chose my ttl method over jiffies in the 
> first
> place because of this problem with jiffies not getting updated. What
> would be the best way to fix this problem? The ttl method I had is not
> that elegant...
Yes, you make a very good point about using jiffies. I've checked in a 
fix to use gettimeofday instead, which does continue to work even with 
interrupts disabled.
Also, the timeout of 5s is arbitrary. We could make it rather less if 
you think that makes sense.
 -- Keir


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