From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chao Peng Subject: Re: [PATCH v2 3/7] x86: detect and initialize Intel CAT feature Date: Mon, 23 Mar 2015 16:36:40 +0800 Message-ID: <20150323083640.GJ5371@pengc-linux.bj.intel.com> References: <1426761695-12545-1-git-send-email-chao.p.peng@linux.intel.com> <1426761695-12545-4-git-send-email-chao.p.peng@linux.intel.com> <1426769087.2560.123.camel@citrix.com> <550ADEB6020000780006BA5B@mail.emea.novell.com> Reply-To: Chao Peng Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <550ADEB6020000780006BA5B@mail.emea.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: Wei Liu , Ian Campbell , Andrew Cooper , Dario Faggioli , "xen-devel@lists.xen.org" , "will.auld@intel.com" , Stefano Stabellini , Ian Jackson , "dgdegra@tycho.nsa.gov" , "Keir (Xen.org)" List-Id: xen-devel@lists.xenproject.org On Thu, Mar 19, 2015 at 01:35:34PM +0000, Jan Beulich wrote: > >>> On 19.03.15 at 13:44, wrote: > > On Thu, 2015-03-19 at 18:41 +0800, Chao Peng wrote: > > > >> diff --git a/docs/misc/xen-command-line.markdown > > b/docs/misc/xen-command-line.markdown > >> index 63871cb..768c55f 100644 > >> --- a/docs/misc/xen-command-line.markdown > >> +++ b/docs/misc/xen-command-line.markdown > >> @@ -1090,9 +1090,9 @@ This option can be specified more than once (up to 8 > > times at present). > >> > `= ` > >> > >> ### psr (Intel) > >> -> `= List of ( cmt: | rmid_max: )` > >> +> `= List of ( cmt: | rmid_max: | cat: | > > num_sockets: )` > >> > > As Tim, I also don't like the 'num_sockets' part of the interface. > > > > Actually, I'm not sure I understand what the idea behind this parameter > > is. You say: > > > >> +* Cache Alllocation Technology (Broadwell and later). Information regarding > >> + the cache allocation. > >> + * `cat` instructs Xen to enable/disable Cache Allocation Technology. > >> + * `num_sockets` indicates the number of available sockets for CAT feature > >> + detection. All the sockets up to num_sockets will be checked for CAT > >> + feature. > >> > > What it the use case of specifying, say, num_sockets=2, on a 4 socket > > system? > > > > Is it for making it possible for the user to disable the feature on some > > of the socket? If yes, I think it does make sense, but then why always > > the last ones? shouldn't this be a list of socket IDs? > > I had asked about this before, and the answer was that this is to > _extend_ the range of sockets, to cover the CPU hotplug case. But > of course I could see ways to at least default the count to something > reasonable even taking hotplug into account (like taking the boot > time CPUs-per-socket value and dividing nr_cpu_ids by that value). Sounds reasonable. I will adopt this suggestion and eliminate the necessary to introduce a boot option like "num_sockets". Chao