From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dario Faggioli Subject: Re: schedulers and topology exposing questions Date: Thu, 28 Jan 2016 15:10:57 +0000 Message-ID: <1453993857.26691.32.camel@citrix.com> References: <20160122165423.GA8595@elena.ufimtseva> <56A756C0.20501@citrix.com> <20160127143303.GA1094@char.us.oracle.com> <56A8DDC9.4080307@citrix.com> <20160127152701.GF552@char.us.oracle.com> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============8181698053892938684==" Return-path: In-Reply-To: <20160127152701.GF552@char.us.oracle.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: Konrad Rzeszutek Wilk , George Dunlap Cc: Elena Ufimtseva , george.dunlap@eu.citrix.com, joao.m.martins@oracle.com, boris.ostrovsky@oracle.com, xen-devel@lists.xen.org List-Id: xen-devel@lists.xenproject.org --===============8181698053892938684== Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="=-Npl6LeQv+2NdronjRzo0" --=-Npl6LeQv+2NdronjRzo0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, 2016-01-27 at 10:27 -0500, Konrad Rzeszutek Wilk wrote: > On Wed, Jan 27, 2016 at 03:10:01PM +0000, George Dunlap wrote: > >=C2=A0 > > I'm not sure I understand the situation right, but it sounds a bit > > like > > what you're seeing is just a quirk of the fact that Linux doesn't > > always > > send IPIs to wake other processes up (either by design or by > > accident), >=20 > It does and it does not :-) >=20 > > but relies on scheduling timers to check for work to > > do.=C2=A0=C2=A0Presumably >=20 > It .. I am not explaining it well. The Linux kernel scheduler when > called for 'schedule' (from the UDP sendmsg) would either pick the > next > appliction and do a context swap - of if there were none - go to > sleep. > [Kind of - it also may do an IPI to the other CPU if requested ,but > that requires > some hints from underlaying layers] > Since there were only two apps on the runqueue - udp sender and udp > receiver > it would run them back-to back (this is on baremetal) >=20 > However if SMT was not exposed - the Linux kernel scheduler would put > those > on each CPU runqueue. Meaning each CPU only had one app on its > runqueue. >=20 > Hence no need to do an context switch. > [unless you modified the UDP message to have a timeout, then it would > send an IPI] > So, may I ask what piece of (Linux) code are we actually talking about? Because I had a quick look, and could not find where what you describe happens.... 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) --=-Npl6LeQv+2NdronjRzo0 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 iEYEABECAAYFAlaqL4EACgkQk4XaBE3IOsS+QACghlgTlqqRs8ss+hUZxVH2ZVGw 2SYAoKtHCQF4bvXMbkX38I0QfPluq+uw =VY+a -----END PGP SIGNATURE----- --=-Npl6LeQv+2NdronjRzo0-- --===============8181698053892938684== 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 --===============8181698053892938684==--