* [Qemu-devel] [PATCH] sysemu: support up to 1024 vCPUs
@ 2016-05-11 14:00 Greg Kurz
2016-05-11 14:20 ` Igor Mammedov
0 siblings, 1 reply; 3+ messages in thread
From: Greg Kurz @ 2016-05-11 14:00 UTC (permalink / raw)
To: Paolo Bonzini; +Cc: Igor Mammedov, qemu-ppc, qemu-devel, David Gibson
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
Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
---
This was tested with a pseries guest only. I'd like to know if it is okay
for other platforms.
include/sysemu/sysemu.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h
index 38fb3cad35e1..89d742caa477 100644
--- a/include/sysemu/sysemu.h
+++ b/include/sysemu/sysemu.h
@@ -185,7 +185,7 @@ extern int mem_prealloc;
*
* Note that cpu->get_arch_id() may be larger than MAX_CPUMASK_BITS.
*/
-#define MAX_CPUMASK_BITS 255
+#define MAX_CPUMASK_BITS 1024
#define MAX_OPTION_ROMS 16
typedef struct QEMUOptionRom {
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [Qemu-devel] [PATCH] sysemu: support up to 1024 vCPUs
2016-05-11 14:00 [Qemu-devel] [PATCH] sysemu: support up to 1024 vCPUs Greg Kurz
@ 2016-05-11 14:20 ` Igor Mammedov
2016-05-11 15:20 ` Greg Kurz
0 siblings, 1 reply; 3+ messages in thread
From: Igor Mammedov @ 2016-05-11 14:20 UTC (permalink / raw)
To: Greg Kurz; +Cc: Paolo Bonzini, qemu-ppc, qemu-devel, David Gibson
On Wed, 11 May 2016 16:00:04 +0200
Greg Kurz <gkurz@linux.vnet.ibm.com> wrote:
> 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
>
> Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
> ---
>
> This was tested with a pseries guest only. I'd like to know if it is okay
> for other platforms.
#git grep MAX_CPUMASK_BITS
...
hw/arm/virt.c: mc->max_cpus = MAX_CPUMASK_BITS;
hw/ppc/spapr.c: mc->max_cpus = MAX_CPUMASK_BITS;
...
you probably don't want to change all those to 1024,
see/review a similar patch where I bump it upto 288 bits
https://lists.gnu.org/archive/html/qemu-devel/2016-05/msg01101.html
in addition where does 1024 come from?
is pseries capable to provide that many CPUs?
>
> include/sysemu/sysemu.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h
> index 38fb3cad35e1..89d742caa477 100644
> --- a/include/sysemu/sysemu.h
> +++ b/include/sysemu/sysemu.h
> @@ -185,7 +185,7 @@ extern int mem_prealloc;
> *
> * Note that cpu->get_arch_id() may be larger than MAX_CPUMASK_BITS.
> */
> -#define MAX_CPUMASK_BITS 255
> +#define MAX_CPUMASK_BITS 1024
>
> #define MAX_OPTION_ROMS 16
> typedef struct QEMUOptionRom {
>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [Qemu-devel] [PATCH] sysemu: support up to 1024 vCPUs
2016-05-11 14:20 ` Igor Mammedov
@ 2016-05-11 15:20 ` Greg Kurz
0 siblings, 0 replies; 3+ messages in thread
From: Greg Kurz @ 2016-05-11 15:20 UTC (permalink / raw)
To: Igor Mammedov; +Cc: Paolo Bonzini, qemu-ppc, qemu-devel, David Gibson
On Wed, 11 May 2016 16:20:08 +0200
Igor Mammedov <imammedo@redhat.com> wrote:
> On Wed, 11 May 2016 16:00:04 +0200
> Greg Kurz <gkurz@linux.vnet.ibm.com> wrote:
>
> > 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
> >
> > Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
> > ---
> >
> > This was tested with a pseries guest only. I'd like to know if it is okay
> > for other platforms.
> #git grep MAX_CPUMASK_BITS
> ...
> hw/arm/virt.c: mc->max_cpus = MAX_CPUMASK_BITS;
> hw/ppc/spapr.c: mc->max_cpus = MAX_CPUMASK_BITS;
> ...
>
> you probably don't want to change all those to 1024,
Well, at least the spapr one :)
> see/review a similar patch where I bump it upto 288 bits
> https://lists.gnu.org/archive/html/qemu-devel/2016-05/msg01101.html
>
Indeed... I should set it to 255 in hw/arm/virt.c. Thanks for pointing
that out.
>
> in addition where does 1024 come from?
All PowerPC distros I could check support either 1024 (PowerKVM,
Fedora) or 2048 (Ubuntu, RHEL7) vCPUs in KVM.
I've chosen 1024 because of PowerKVM :)
> is pseries capable to provide that many CPUs?
>
Yes.
> >
> > include/sysemu/sysemu.h | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h
> > index 38fb3cad35e1..89d742caa477 100644
> > --- a/include/sysemu/sysemu.h
> > +++ b/include/sysemu/sysemu.h
> > @@ -185,7 +185,7 @@ extern int mem_prealloc;
> > *
> > * Note that cpu->get_arch_id() may be larger than MAX_CPUMASK_BITS.
> > */
> > -#define MAX_CPUMASK_BITS 255
> > +#define MAX_CPUMASK_BITS 1024
> >
> > #define MAX_OPTION_ROMS 16
> > typedef struct QEMUOptionRom {
> >
>
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2016-05-11 15:21 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2016-05-11 14:00 [Qemu-devel] [PATCH] sysemu: support up to 1024 vCPUs Greg Kurz
2016-05-11 14:20 ` Igor Mammedov
2016-05-11 15:20 ` Greg Kurz
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.