From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Cooper Subject: Re: [PATCH 0/2] make hypercall preemption checks consistent Date: Tue, 4 Mar 2014 11:52:06 +0000 Message-ID: <5315BE66.5030903@citrix.com> References: <5315C5370200007800120CE4@nat28.tlf.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta14.messagelabs.com ([193.109.254.103]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1WKntJ-0002dY-Lq for xen-devel@lists.xenproject.org; Tue, 04 Mar 2014 11:52:09 +0000 In-Reply-To: <5315C5370200007800120CE4@nat28.tlf.novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Jan Beulich Cc: xen-devel , Keir Fraser List-Id: xen-devel@lists.xenproject.org On 04/03/14 11:21, Jan Beulich wrote: > - never preempt on the first iteration (ensure forward progress) > - never preempt on the last iteration (pointless/wasteful) > - do cheap checks first > > 1: common: make hypercall preemption checks consistent > 2: x86: make hypercall preemption checks consistent > > Signed-off-by: Jan Beulich All in all, this is a good improvement over what is currently present. However, given the overhead of creating continuations (particularly for 32bit HVM guests, which have been seen to unconditionally fail the preemption check by the time the compat layer has run), some of these operations would probably be better having more than a single guaranteed operation. ~Andrew