Re: [Qemu-devel] [RFC PATCH v2 21/23] spapr: Initialize hotplug memory address space

[Igor Mammedov]

On Mon, 13 Apr 2015 19:57:05 +0530
Bharata B Rao <address@hidden> wrote:

> On Mon, Apr 13, 2015 at 04:04:24PM +0200, Igor Mammedov wrote:
> > On Mon, 13 Apr 2015 08:29:33 +0530
> > Bharata B Rao <address@hidden> wrote:
> > 
> > > On Wed, Mar 25, 2015 at 04:58:18PM +1100, David Gibson wrote:
> > > > On Mon, Mar 23, 2015 at 07:06:02PM +0530, Bharata B Rao wrote:
> > > > > Initialize a hotplug memory region under which all the hotplugged
> > > > > memory is accommodated. Also enable memory hotplug by setting
> > > > > CONFIG_MEM_HOTPLUG.
> > > > > 
> > > > > Modelled on i386 memory hotplug.
> > > > > 
> > > > > Signed-off-by: Bharata B Rao <address@hidden>
> > > > > ---
> > > > >  default-configs/ppc64-softmmu.mak |  1 +
> > > > >  hw/ppc/spapr.c                    | 50 
> > > > > +++++++++++++++++++++++++++++++++++++++
> > > > >  include/hw/ppc/spapr.h            | 12 ++++++++++
> > > > >  3 files changed, 63 insertions(+)
> > > > > 
> > > > > diff --git a/default-configs/ppc64-softmmu.mak 
> > > > > b/default-configs/ppc64-softmmu.mak
> > > > > index 22ef132..16b3011 100644
> > > > > --- a/default-configs/ppc64-softmmu.mak
> > > > > +++ b/default-configs/ppc64-softmmu.mak
> > > > > @@ -51,3 +51,4 @@ CONFIG_XICS_KVM=$(and 
> > > > > $(CONFIG_PSERIES),$(CONFIG_KVM))
> > > > >  # For PReP
> > > > >  CONFIG_MC146818RTC=y
> > > > >  CONFIG_ISA_TESTDEV=y
> > > > > +CONFIG_MEM_HOTPLUG=y
> > > > > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > > > > index 3e56d9e..e43bb49 100644
> > > > > --- a/hw/ppc/spapr.c
> > > > > +++ b/hw/ppc/spapr.c
> > > > > @@ -125,8 +125,13 @@ struct sPAPRMachineState {
> > > > >  
> > > > >      /*< public >*/
> > > > >      char *kvm_type;
> > > > > +    ram_addr_t hotplug_memory_base;
> > > > > +    MemoryRegion hotplug_memory;
> > > > > +    bool enforce_aligned_dimm;
> > > > >  };
> > > > >  
> > > > > +#define SPAPR_MACHINE_ENFORCE_ALIGNED_DIMM "enforce-aligned-dimm"
> > > > 
> > > > What's the rationale for including this option?
> > > 
> > > I couldn't see any use, but added it to be similar with x86. May be Igor
> > > can tell us ?
> > at least on x86 KVM requires memory region be aligned (otherwise it would 
> > abort)
> > and also performance wise it's better to map regions at offsets aligned at
> > backend page size (especially applicable for hugepages).
> > 
> > so region base on x86 is 1Gb aligned to support upto 1Gb hugepages.
> 
> My question was specifically about the enforce-aligned-dimm object property
> that has a get method. I was wondering where this property is consumed. All
> I could see is that PCMachineState.enforce_aligned_dimm used/referenced
> directly.
I think that you don't heed it, it was introduce to to keep memory layout
compatible with old machine types that didn't have aligned memhp region.

Since there is nothing to keep compatible in this target, you can just
drop property and always align region as fit for spapr.

> 
> > 
> > > 
> > > Regards,
> > > Bharata.
> > > 
>