On Mon, 27 Feb 2017 12:09:53 +1100 David Gibson <da...@gibson.dropbear.id.au> wrote:
> On Fri, Feb 24, 2017 at 10:13:50AM +0100, Greg Kurz wrote: > > On Fri, 24 Feb 2017 15:55:31 +1100 > > Alexey Kardashevskiy <a...@ozlabs.ru> wrote: > > > > > From: Greg Kurz <gk...@linux.vnet.ibm.com> > > > > > > Some systems can already provide more than 255 hardware threads. > > > > > > Bumping the QEMU limit to 1024 seems reasonable: > > > - it has no visible overhead in top; > > > - the limit itself has no effect on hot paths. > > > > > > Cc: Greg Kurz <gk...@linux.vnet.ibm.com> > > > Signed-off-by: Alexey Kardashevskiy <a...@ozlabs.ru> > > > --- > > > > > > With ulimit -u/-n bumped (nproc and nofile), I was able to boot a guest > > > with 1024 CPUs, both with threads=1 and threads=8. > > > > > > 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? > No but I'll try again with the current code and I'll have a closer look. > > > > > --- > > > hw/ppc/spapr.c | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > 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 = ppc_spapr_init; > > > mc->reset = ppc_spapr_reset; > > > mc->block_default_type = IF_SCSI; > > > - mc->max_cpus = 255; > > > + mc->max_cpus = 1024; > > > mc->no_parallel = 1; > > > mc->default_boot_order = ""; > > > mc->default_ram_size = 512 * M_BYTE; > > > > > > >
pgpRd_L1DKAfM.pgp
Description: OpenPGP digital signature
