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From: Gerd Hoffmann <kraxel@redhat.com>
Date: Tue, 02 Aug 2016 13:35:49 +0200
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Subject: Re: [Qemu-devel] [PATCH 1/1] ehci: faster frame index calculation
 for skipped frames
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To: "Denis V. Lunev" <den@openvz.org>
Cc: qemu-devel@nongnu.org, Evgeny Yakovlev <eyakovlev@virtuozzo.com>

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.
>=20
> 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.
>=20
> 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.
>=20
> This change makes ehci_update_frindex execute in constant time.
>=20

queued up for 2.7

thanks,
  Gerd