Re: [RFC v1 3/3] hw/arm/virt-acpi-build.c: Enable CPU cache topology

[Jonathan Cameron]

On Tue, 30 Jan 2024 05:03:15 +0000
JeeHeng Sia <jeeheng.sia@starfivetech.com> wrote:

> > -----Original Message-----
> > From: Jonathan Cameron <Jonathan.Cameron@Huawei.com>
> > Sent: Monday, January 29, 2024 7:08 PM
> > To: JeeHeng Sia <jeeheng.sia@starfivetech.com>
> > Cc: qemu-devel@nongnu.org; qemu-arm@nongnu.org; qemu-riscv@nongnu.org; 
> > mst@redhat.com; imammedo@redhat.com;
> > anisinha@redhat.com; shannon.zhaosl@gmail.com; peter.maydell@linaro.org; 
> > sunilvl@ventanamicro.com; palmer@dabbelt.com;
> > alistair.francis@wdc.com; bin.meng@windriver.com; liwei1518@gmail.com; 
> > dbarboza@ventanamicro.com;
> > zhiwei_liu@linux.alibaba.com
> > Subject: Re: [RFC v1 3/3] hw/arm/virt-acpi-build.c: Enable CPU cache 
> > topology
> > 
> > On Mon, 29 Jan 2024 00:14:23 -0800
> > Sia Jee Heng <jeeheng.sia@starfivetech.com> wrote:
> >   
> > > Introduced a 3-layer cache for the ARM virtual machine.
> > >
> > > Signed-off-by: Sia Jee Heng <jeeheng.sia@starfivetech.com>  
> > 
> > There are a bunch of CPU registers that also need updating to reflect the
> > described cache.
> > https://lore.kernel.org/qemu-devel/20230808115713.2613-3-Jonathan.Cameron@huawei.com/
> > It's called HACK for a reason ;)
> > But there is some discussion about this issue in the thread.
> > 
> > The l1 etc also needs to reflect the CPU model.  This stuff needs to match.
> > Wrong information being passed to a VM is probably worse than no 
> > information.
> > 
> > Whilst I plan to circle back to the MPAM support (perhaps next month) there
> > is a lot more to be done here before we have useful cache descriptions for
> > guests.  
> Thanks for the info. I will spend time to look into.
> > 
> > Jonathan
> >   
> > > ---
> > >  hw/arm/virt-acpi-build.c | 44 +++++++++++++++++++++++++++++++++++++++-
> > >  1 file changed, 43 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c
> > > index 17aeec7a6f..c57067cd63 100644
> > > --- a/hw/arm/virt-acpi-build.c
> > > +++ b/hw/arm/virt-acpi-build.c
> > > @@ -426,6 +426,48 @@ build_iort(GArray *table_data, BIOSLinker *linker, 
> > > VirtMachineState *vms)
> > >      g_array_free(its_idmaps, true);
> > >  }
> > >
> > > +static void pptt_setup(GArray *table_data, BIOSLinker *linker, 
> > > MachineState *ms,
> > > +                       const char *oem_id, const char *oem_table_id)
> > > +{
> > > +    CPUCaches default_cache_info = {
> > > +        .l1d_cache = &(CPUCacheInfo) {
> > > +            .type = DATA_CACHE,
> > > +            .size = 64 * KiB,
> > > +            .line_size = 64,
> > > +            .associativity = 4,
> > > +            .sets = 256,
> > > +            .attributes = 0x02,
> > > +        },
> > > +        .l1i_cache = &(CPUCacheInfo) {
> > > +            .type = INSTRUCTION_CACHE,
> > > +            .size = 64 * KiB,
> > > +            .line_size = 64,
> > > +            .associativity = 4,
> > > +            .sets = 256,
> > > +            .attributes = 0x04,  
> > 
> > This is the duplication I commented on in patch 1.
> > The bit set there is the one to indicate it's an instruction
> > cache and we have type doing that as well.  
> But this gives a great readability, no?

Not really no. If .type and attributes end up out of agreement with each
other it will be non obvious.

You could do 
                .attributes {
                        .type = INSTRUCTION_CACHE,
                        .other things ...
                }

if you want to list the type clearly and still maintain the info that
this ends up in attributes.


> > 
> >   
> > > +        },
> > > +        .l2_cache = &(CPUCacheInfo) {
> > > +            .type = UNIFIED_CACHE,
> > > +            .size = 2048 * KiB,
> > > +            .line_size = 64,
> > > +            .associativity = 8,
> > > +            .sets = 4096,
> > > +            .attributes = 0x0a,
> > > +        },
> > > +        .l3_cache = &(CPUCacheInfo) {
> > > +            .type = UNIFIED_CACHE,
> > > +            .size = 4096 * KiB,
> > > +            .line_size = 64,
> > > +            .associativity = 8,
> > > +            .sets = 8192,
> > > +            .attributes = 0x0a,
> > > +        },
> > > +    };
> > > +
> > > +    build_pptt(table_data, linker, ms, oem_id, oem_table_id,
> > > +               &default_cache_info);
> > > +}
> > > +
> > >  /*
> > >   * Serial Port Console Redirection Table (SPCR)
> > >   * Rev: 1.07
> > > @@ -912,7 +954,7 @@ void virt_acpi_build(VirtMachineState *vms, 
> > > AcpiBuildTables *tables)
> > >
> > >      if (!vmc->no_cpu_topology) {
> > >          acpi_add_table(table_offsets, tables_blob);
> > > -        build_pptt(tables_blob, tables->linker, ms,
> > > +        pptt_setup(tables_blob, tables->linker, ms,
> > >                     vms->oem_id, vms->oem_table_id);
> > >      }
> > >  
>