Re: [Qemu-devel] [PATCH qemu] sysemu: support up to 1024 vCPUs

[Igor Mammedov <imammedo@redhat.com>]

On Wed, 19 Oct 2016 10:39:12 +1100
Alexey Kardashevskiy <aik@ozlabs.ru> wrote:

> On 18/10/16 22:00, Igor Mammedov wrote:
> > On Tue, 11 Oct 2016 09:19:10 +1100
> > Alexey Kardashevskiy <aik@ozlabs.ru> wrote:
> >   
> >> Ping, anyone?  
> > I have a similar patch
> > http://patchwork.ozlabs.org/patch/681709/
> > which bumps limit to 288 and does a little bit more
> > so it wouldn't affect current users.  
> 
> Why 288 (not oldlimit<<n)? :)
That's how many vCPU we plan to support for target-i386.


> What does happen to the Greg's patch now?
it could be amended to apply top of above patch,

where it would change not only MAX_CPUMASK_BITS but also
maxcpus in ppc target since above patch unties maxcpus
from MAX_CPUMASK_BITS for all targets.

So followup increases of MAX_CPUMASK_BITS won't affect
other targets.

> 
> 
> > 
> > After that's merged, I plan to get rid of this limit and
> > make that part of numa parsing code dynamic so that it
> > wouldn't impose such limit/any limits on target code.
> >   
> >>
> >>
> >> On 04/10/16 11:33, Alexey Kardashevskiy wrote:  
> >>> From: Greg Kurz <gkurz@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.
> >>>
> >>> Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
> >>> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> >>> ---
> >>>  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 ef2c50b..2ec0bd8 100644
> >>> --- a/include/sysemu/sysemu.h
> >>> +++ b/include/sysemu/sysemu.h
> >>> @@ -173,7 +173,7 @@ 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 {
> >>>     
> >>
> >>  
> >   
> 
>