From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dario Faggioli Subject: Re: [PATCH v4 03/15] libxl: introduce libxl_get_nr_cpus() Date: Tue, 3 Dec 2013 19:19:14 +0100 Message-ID: <1386094754.5338.352.camel@Solace> References: <20131122183332.11200.20231.stgit@Solace> <20131122185658.11200.13074.stgit@Solace> <21150.6530.28766.823281@mariner.uk.xensource.com> <1386093157.5338.337.camel@Solace> <21150.6842.156846.991072@mariner.uk.xensource.com> <529E1E46.2060106@eu.citrix.com> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============5807206051131891040==" Return-path: In-Reply-To: <529E1E46.2060106@eu.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: George Dunlap Cc: Marcus Granado , Keir Fraser , Ian Campbell , Li Yechen , Andrew Cooper , Juergen Gross , Ian Jackson , xen-devel@lists.xen.org, Jan Beulich , Justin Weaver , Matt Wilson , Elena Ufimtseva List-Id: xen-devel@lists.xenproject.org --===============5807206051131891040== Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="=-do4n0j3GtEsWEy5IYaD/" --=-do4n0j3GtEsWEy5IYaD/ Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On mar, 2013-12-03 at 18:09 +0000, George Dunlap wrote: > On 12/03/2013 05:54 PM, Ian Jackson wrote: > > Dario Faggioli writes ("Re: [PATCH v4 03/15] libxl: introduce libxl_get= _nr_cpus()"): > >> On mar, 2013-12-03 at 17:48 +0000, Ian Jackson wrote: > >>> This number might be out of date as soon as it is read, won't it ? > >> > >> Quite possible, yes. > >> > >> So, are you suggesting that we shouldn't even allow the user to read i= t? > >> Or that I should mention that in the comment? (Or something else?) > > > > Perhaps I didn't explain my concerns clearly enough. > > > > I wonder what is it for ? Isn't it difficult to use correctly ? >=20 > Dario uses it in the new version of libxl_vcpu_set_affinity() to limit= =20 > what was considered an "unreachable cpu" in its warning. (v5 14/17)=20 > That is, if you set the affinity to 1111111111111111111111..., and there= =20 > are only 4 pcpus, it will return 111100000..... These don't match, and= =20 > yet there are no unreachable cpus. So it asks nr_cpus first, then only= =20 > compares bits 1..[nr_cpus-1]. >=20 Yes, and also in the new dryrun_only mode I'm introducing for `xl vcpu-pin', as print_bitmap() in xl wants to know the total number of pcpus, so that, if the mask is <11110000>, but we only have 4 pcpus, it can print "all". > I'm not sure how often that would change, but if there was a race, I=20 > think it would just be a spurious error message (or lack thereof). >=20 Exactly. Also, as mentioned in the other e-mail I just sent, I'm up for trying to figure out a better way to handle this, as soon as 4.5 begins. Thanks and Regards, Dario --=20 <> (Raistlin Majere) ----------------------------------------------------------------- Dario Faggioli, Ph.D, http://about.me/dario.faggioli Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK) --=-do4n0j3GtEsWEy5IYaD/ Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.15 (GNU/Linux) iEYEABECAAYFAlKeIKMACgkQk4XaBE3IOsSASwCgpLi1ih/cLgJzUAKmRzvDUTza RQoAnR6Xn3ZB8TYxiZKOm0jmE0mLcNyC =q1UY -----END PGP SIGNATURE----- --=-do4n0j3GtEsWEy5IYaD/-- --===============5807206051131891040== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel --===============5807206051131891040==--