From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keir Fraser Subject: Re: Can we remove the logic of preventing MSI irq storms Date: Thu, 14 Jul 2011 08:06:59 +0100 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Haitao Shan Cc: xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org On 14/07/2011 07:43, "Haitao Shan" wrote: > Hi, Keir, > > As you may remember (see c/s 17960), Xen implemented the logic of > preventing MSI irq storms. The reason of the IRQ storm at that time is > still unknown. But the logic is definitely needed at that time since > that NIC is the only device at my hand to test MSI. > The idea is simple: mask the second MSI interrupt when the first one > is still in processing. For HVM guests, we hooked at guest EOI write > to determime whether the first MSI is serviced already. > > However, recently we find the logic has negative impact on 10G NIC > performance (assigned to guest). The logic lowers the interrupt > frequency that Xen can handle. It is a problem when the device is > generating too many interrupts as seen in this 10G NIC. > > And now there is IRQ rate limit logic in Xenm which can also help to > prevent IRQ storms. > > Given all the above, do you think it is time to remove the logic of > preventing MSI IRQ storm? I'd be happy to see it go. -- Keir > Shan Haitao