From mboxrd@z Thu Jan 1 00:00:00 1970 From: Julien Grall Subject: Re: [PATCH V6 00/10] Support more than 8 vcpus on arm64 with GICv3 Date: Fri, 5 Jun 2015 15:37:08 +0100 Message-ID: <5571B414.7090105@citrix.com> References: <1433163388-16970-1-git-send-email-cbz@baozis.org> <1433513313.7108.316.camel@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta3.messagelabs.com ([195.245.230.39]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1Z0skm-0000dh-6Q for xen-devel@lists.xenproject.org; Fri, 05 Jun 2015 14:37:48 +0000 In-Reply-To: <1433513313.7108.316.camel@citrix.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: Ian Campbell , Chen Baozi Cc: Julien Grall , xen-devel@lists.xenproject.org, Chen Baozi List-Id: xen-devel@lists.xenproject.org On 05/06/15 15:08, Ian Campbell wrote: > On Mon, 2015-06-01 at 20:56 +0800, Chen Baozi wrote: >> From: Chen Baozi >> >> Currently the number of vcpus on arm64 with GICv3 is limited up to 8 due >> to the fixed size of redistributor mmio region. > > Are we talking about only guests here or are hosts impacted too somehow? Guest only. The GICv3 driver should already supports 128 CPUs (though never tested). >> Increasing the size >> makes the number expand to 16 because of AFF0 restriction on GICv3. > > Can you give a reference for this please? "AFF0" doesn't appear anywhere > in my gic v3 spec, and "4.2.2 Interrupt Routing in GICv3 Systems" > implies 256 processors at each affinity level (which is what I > expected). 5.7.29 ICC_SGI0R_EL1, ICC_SGI1R_EL1 and ICC_ASGI1R_EL1: "Note: this restricts distribution of SGIs to the first 16 processors of an affinity 1 cluster". Therefore any CPU using AFF0 >= 16 would never receive SGI. FWIW, Linux is shouting loud when the AFF0 is too high. Xen does the same thing in the GICv3 drivers. Regards, -- Julien Grall