Re: [Qemu-devel] [PATCH 1/1] ehci: faster frame index calculation for skipped frames

[Gerd Hoffmann]

On Mi, 2016-07-27 at 19:55 +0300, Denis V. Lunev wrote:
> ehci_update_frindex takes time linearly proportional to a number
> of uframes to calculate new frame index and raise FLR interrupts,
> which is a problem for large amounts of uframes.
> 
> If we experience large delays between echi timer callbacks (i.e.
> because
> other periodic handlers have taken a lot of time to complete) we
> get a lot of skipped frames which then delay ehci timer callback more
> and this leads to deadlocking the system when ehci schedules next
> callback to be too soon.
> 
> Observable behaviour is qemu consuming 100% host CPU time while guest
> is unresponsive. This misbehavior could happen for a while and QEMU
> does
> not get out from this state automatically without the patch.
> 
> This change makes ehci_update_frindex execute in constant time.
> 

queued up for 2.7

thanks,
  Gerd