From mboxrd@z Thu Jan 1 00:00:00 1970 From: George Dunlap Subject: Re: [RFC PATCH 3/7] xen: psr: reserve an RMID for each core Date: Wed, 8 Apr 2015 14:28:41 +0100 Message-ID: <55252D09.6070307@eu.citrix.com> References: <20150404020423.22875.23590.stgit@Solace.station> <20150404021441.22875.9924.stgit@Solace.station> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20150404021441.22875.9924.stgit@Solace.station> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Dario Faggioli , Xen-devel Cc: wei.liu2@citrix.com, Ian.Campbell@citrix.com, andrew.cooper3@citrix.com, Dongxiao Xu , JBeulich@suse.com, Chao Peng List-Id: xen-devel@lists.xenproject.org On 04/04/2015 03:14 AM, Dario Faggioli wrote: > This allows for a new item to be passed as part of the psr= > boot option: "percpu_cmt". If that is specified, Xen tries, > at boot time, to associate an RMID to each core. > > XXX This all looks rather straightforward, if it weren't > for the fact that it is, apparently, more common than > I though to run out of RMID. For example, on a dev box > we have in Cambridge, there are 144 pCPUs and only 71 > RMIDs. Is that because you have 2 sockets? There's no need to keep RMIDs unique across sockets, is there? E.g., socket 0 cpu 0 and socket 1 cpu 0 can have the same RMID, because cache and the MSRs are per-socket. If we're doing things on a per-domain basis, having the same RMID allocated for each socket sort of makes sense; but even then, if you know a domain is only going to run on a given socket, there's no reason in theory we couldn't use same RMID for a different domain on the other socket (assuming it was only going to run on the other socket). One advantage of doing things of a per-vcpu level is that you wouldn't have to worry about inter-socket RMID issues. -George