From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:58308) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ciAGy-0007iR-6Y for qemu-devel@nongnu.org; Sun, 26 Feb 2017 20:38:45 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ciAGv-0003I0-2q for qemu-devel@nongnu.org; Sun, 26 Feb 2017 20:38:44 -0500 Date: Mon, 27 Feb 2017 12:09:53 +1100 From: David Gibson Message-ID: <20170227010953.GN17615@umbus.fritz.box> References: <20170224045531.7026-1-aik@ozlabs.ru> <20170224101350.043b97a6@bahia.lan> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="RL02At1kLqUPtqvA" Content-Disposition: inline In-Reply-To: <20170224101350.043b97a6@bahia.lan> Subject: Re: [Qemu-devel] [Qemu-ppc] [PATCH qemu] sysemu: support up to 1024 vCPUs List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Greg Kurz Cc: Alexey Kardashevskiy , qemu-devel@nongnu.org, qemu-ppc@nongnu.org, Greg Kurz --RL02At1kLqUPtqvA Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Fri, Feb 24, 2017 at 10:13:50AM +0100, Greg Kurz wrote: > On Fri, 24 Feb 2017 15:55:31 +1100 > Alexey Kardashevskiy wrote: >=20 > > From: Greg Kurz > >=20 > > Some systems can already provide more than 255 hardware threads. > >=20 > > Bumping the QEMU limit to 1024 seems reasonable: > > - it has no visible overhead in top; > > - the limit itself has no effect on hot paths. > >=20 > > Cc: Greg Kurz > > Signed-off-by: Alexey Kardashevskiy > > --- > >=20 > > With ulimit -u/-n bumped (nproc and nofile), I was able to boot a guest > > with 1024 CPUs, both with threads=3D1 and threads=3D8. > >=20 > > It takes time though - 3:15 to get to the guest shell but it is probably > > expected on 160-threads machine. Yes, I'd expect so, that's a lot of overcommit. Plus, switching from one vcpu to another on the same host thread will, IIRC, require two full partition switches, which are pretty slow on Power. > I remember something similiar at the time... also I had to give more > RAM to the guest to be able to run 1024 CPUs (sth like 6 gigs versus > 512 megs for 1 CPU). With the same amount of guest RAM, each extra CPU > would cause the memory used by QEMU to grow about 8 megs. Hm... that seems like rather a lot. Any idea why? >=20 > > --- > > hw/ppc/spapr.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > >=20 > > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c > > index e465d7ac98..46b81a625d 100644 > > --- a/hw/ppc/spapr.c > > +++ b/hw/ppc/spapr.c > > @@ -2712,7 +2712,7 @@ static void spapr_machine_class_init(ObjectClass = *oc, void *data) > > mc->init =3D ppc_spapr_init; > > mc->reset =3D ppc_spapr_reset; > > mc->block_default_type =3D IF_SCSI; > > - mc->max_cpus =3D 255; > > + mc->max_cpus =3D 1024; > > mc->no_parallel =3D 1; > > mc->default_boot_order =3D ""; > > mc->default_ram_size =3D 512 * M_BYTE; >=20 >=20 --=20 David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson --RL02At1kLqUPtqvA Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQIcBAEBCAAGBQJYs3xhAAoJEGw4ysog2bOSum4QAOLSbf07Zu0dOKBBwqKz6uA1 VOsqDiGu/mGddyjgy/FVBfZc7JmM099b9qhXfBA15+CStcOmxN5a3EnYsrzjHuoh 8kuRjC1dGwuhGFnOsE/qoTrWYa2sFEQY3VvVNJwnoX4pcUbsUV8FZhocD61WCldQ ibOOzBNe3SKy5FZZ3v8VQPHgnCGXOmMueZNdc+aMBB+AJzpQoq2wwH6vb22k54f8 VU3TZ6nsrjipUcE74eV/L5WIGtmBELnxOKccFOf+LRnZwvDaLZUPWTLTaAGX1j7L /dMrDGZBQ5YlYFQn7MldlAp3OZghudlasCFhPIUTNRE2i9+mafWIa3iqVpWsnP8d M2kyOzoaMCqf6fsa981vvS9Y7XSAEQV+/SZ7VmQV8wG+97agYyW6rt5URnvZ+Zpe UFOA1Y5DbJk2OnLKFa/0O1bdhsv9aA0448kCm6OHexomKfLiJPi+pLr7UQTi1xdZ XU3eQkLZxcLaNuJNwgbVbVMqCMvQ0duuP63xRPsY43lOXNLIexmlhnMW0IEM5ir8 xTHCdmriIjyukrt1PuxHbLjlnsCD11qIiUiOnBwpNd8mo5bE8AdB0ROvZgapUBuZ 9K6FqEBn1Whs0ka9sodgSGM0XKmRs4hYgBd8Dn4HkWN0YPxsQ+dsduDeiRjGVzx8 DT4vo3W3Eunv8aRB2/A6 =aj12 -----END PGP SIGNATURE----- --RL02At1kLqUPtqvA--