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Re: [Qemu-devel] [PATCH 2/2] pc: memhp: force gaps between DIMM's GPA
From: |
Igor Mammedov |
Subject: |
Re: [Qemu-devel] [PATCH 2/2] pc: memhp: force gaps between DIMM's GPA |
Date: |
Sun, 27 Sep 2015 15:06:24 +0200 |
On Sun, 27 Sep 2015 13:48:21 +0300
"Michael S. Tsirkin" <address@hidden> wrote:
> On Fri, Sep 25, 2015 at 03:53:12PM +0200, Igor Mammedov wrote:
> > mapping DIMMs non contiguously allows to workaround
> > virtio bug reported earlier:
> > http://lists.nongnu.org/archive/html/qemu-devel/2015-08/msg00522.html
> > in this case guest kernel doesn't allocate buffers
> > that can cross DIMM boundary keeping each buffer
> > local to a DIMM.
> >
> > Suggested-by: Michael S. Tsirkin <address@hidden>
> > Signed-off-by: Igor Mammedov <address@hidden>
> > ---
> > benefit of this workaround is that no guest side
> > changes are required.
>
> That's a hard requirement, I agree.
>
>
> > ---
> > hw/i386/pc.c | 4 +++-
> > hw/i386/pc_piix.c | 3 +++
> > hw/i386/pc_q35.c | 3 +++
> > include/hw/i386/pc.h | 2 ++
> > 4 files changed, 11 insertions(+), 1 deletion(-)
>
> Aren't other architectures besides PC ever affected?
> Do they all allocate all of memory contigious in HVA space?
I'm not sure about other targets I've CCed interested parties.
>
> Also - does the issue only affect hotplugged memory?
Potentially it affects -numa memdev=foo, but however I've
tried I wasn't able to reproduce. We could do it as
separate workaround later if it would affect someone
and virtio is not fixed to handle split buffers by that time.
> Can't the patch be local to pc-dimm (except maybe the
> backwards compatibility thing)?
I think decision about using gaps and its size
should be done by board and not generic pc-dimm.
> > diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> > index 91d134c..c462c4e 100644
> > --- a/hw/i386/pc.c
> > +++ b/hw/i386/pc.c
> > @@ -1629,6 +1629,7 @@ static void pc_dimm_plug(HotplugHandler *hotplug_dev,
> > HotplugHandlerClass *hhc;
> > Error *local_err = NULL;
> > PCMachineState *pcms = PC_MACHINE(hotplug_dev);
> > + PCMachineClass *pcmc = PC_MACHINE_GET_CLASS(pcms);
> > PCDIMMDevice *dimm = PC_DIMM(dev);
> > PCDIMMDeviceClass *ddc = PC_DIMM_GET_CLASS(dimm);
> > MemoryRegion *mr = ddc->get_memory_region(dimm);
> > @@ -1644,7 +1645,8 @@ static void pc_dimm_plug(HotplugHandler *hotplug_dev,
> > goto out;
> > }
> >
> > - pc_dimm_memory_plug(dev, &pcms->hotplug_memory, mr, align, 0,
> > &local_err);
> > + pc_dimm_memory_plug(dev, &pcms->hotplug_memory, mr, align,
> > + pcmc->inter_dimm_gap, &local_err);
> > if (local_err) {
> > goto out;
> > }
> > diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
> > index 3ffb05f..3165667 100644
> > --- a/hw/i386/pc_piix.c
> > +++ b/hw/i386/pc_piix.c
> > @@ -457,11 +457,13 @@ static void pc_xen_hvm_init(MachineState *machine)
> >
> > static void pc_i440fx_machine_options(MachineClass *m)
> > {
> > + PCMachineClass *pcmc = PC_MACHINE_CLASS(m);
> > m->family = "pc_piix";
> > m->desc = "Standard PC (i440FX + PIIX, 1996)";
> > m->hot_add_cpu = pc_hot_add_cpu;
> > m->default_machine_opts = "firmware=bios-256k.bin";
> > m->default_display = "std";
> > + pcmc->inter_dimm_gap = PC_2MB_DIMM_GAP;
> > }
> >
> > static void pc_i440fx_2_5_machine_options(MachineClass *m)
> > @@ -482,6 +484,7 @@ static void pc_i440fx_2_4_machine_options(MachineClass
> > *m)
> > m->alias = NULL;
> > m->is_default = 0;
> > pcmc->broken_reserved_end = true;
> > + pcmc->inter_dimm_gap = 0;
> > SET_MACHINE_COMPAT(m, PC_COMPAT_2_4);
> > }
> >
> > diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
> > index 1b7d3b6..8ad6687 100644
> > --- a/hw/i386/pc_q35.c
> > +++ b/hw/i386/pc_q35.c
> > @@ -360,6 +360,7 @@ static void pc_compat_1_4(MachineState *machine)
> >
> > static void pc_q35_machine_options(MachineClass *m)
> > {
> > + PCMachineClass *pcmc = PC_MACHINE_CLASS(m);
> > m->family = "pc_q35";
> > m->desc = "Standard PC (Q35 + ICH9, 2009)";
> > m->hot_add_cpu = pc_hot_add_cpu;
> > @@ -368,6 +369,7 @@ static void pc_q35_machine_options(MachineClass *m)
> > m->default_display = "std";
> > m->no_floppy = 1;
> > m->no_tco = 0;
> > + pcmc->inter_dimm_gap = PC_2MB_DIMM_GAP;
> > }
> >
> > static void pc_q35_2_5_machine_options(MachineClass *m)
> > @@ -385,6 +387,7 @@ static void pc_q35_2_4_machine_options(MachineClass *m)
> > pc_q35_2_5_machine_options(m);
> > m->alias = NULL;
> > pcmc->broken_reserved_end = true;
> > + pcmc->inter_dimm_gap = 0;
> > SET_MACHINE_COMPAT(m, PC_COMPAT_2_4);
> > }
> >
> > diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h
> > index 6896328..dd6b34a 100644
> > --- a/include/hw/i386/pc.h
> > +++ b/include/hw/i386/pc.h
> > @@ -50,6 +50,7 @@ struct PCMachineState {
> > #define PC_MACHINE_SMM "smm"
> > #define PC_MACHINE_ENFORCE_ALIGNED_DIMM "enforce-aligned-dimm"
> >
> > +#define PC_2MB_DIMM_GAP (1ULL << 21)
> > /**
> > * PCMachineClass:
> > * @get_hotplug_handler: pointer to parent class callback
> > @get_hotplug_handler
>
> Seems somewhat arbitrary. It's aligned later - so won't a 1 byte gap be
> enough?
1 byte should be also enough, since effectively it would kick alignment
adjustment.
The reason why I've picked 2Mb is that QEMU ram allocator allocates
2Mb granularity.
>
> > @@ -60,6 +61,7 @@ struct PCMachineClass {
> >
> > /*< public >*/
> > bool broken_reserved_end;
> > + uint64_t inter_dimm_gap;
> > HotplugHandler *(*get_hotplug_handler)(MachineState *machine,
> > DeviceState *dev);
> > };
> > --
> > 1.8.3.1
[Qemu-devel] [PATCH 1/2] memhp: extend address auto assignment to support gaps, Igor Mammedov, 2015/09/25