From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keir Fraser Subject: Re: [xen-unstable test] 6947: regressions - trouble: broken/fail/pass Date: Mon, 02 May 2011 13:19:45 +0100 Message-ID: References: <4DBEB8FA020000780003F276@vpn.id2.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4DBEB8FA020000780003F276@vpn.id2.novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Jan Beulich Cc: xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org On 02/05/2011 13:00, "Jan Beulich" wrote: >> (3) Restructure the interrupt code to do less work in IRQ context. For >> example tasklet-per-irq, and schedule on the local cpu. Protect a bunch of >> the PIRQ structures with a non-IRQ lock. Would increase interrupt latency if >> the local CPU is interrupted in hypervisor context. I'm not sure about this >> one -- I'm not that happy about the amount of work now done in hardirq >> context, but I'm not sure on the performance impact of deferring the work. > > I'm not inclined to make changes in this area for the purpose at hand > either (again, Linux gets away without this - would have to check how > e.g. KVM gets the TLB flushing done, or whether they don't defer > flushes like we do). Oh, another way would be to make lookup_slot invocations from IRQ context be RCU-safe. Then the radix tree updates would not have to synchronise on the irq_desc lock? And I believe Linux has examples of RCU-safe usage of radix trees -- certainly Linux's radix-tree.h mentions RCU. I must say this would be far more attractive to me than hacking the xmalloc subsystem. That's pretty nasty. -- Keir