Re: [Qemu-devel] [PATCH] arm: virt-acpi: each MADT.GICC entry as enabled unconditionally

[Andrew Jones]

On Fri, Jan 29, 2016 at 10:59:32PM +0800, Shannon Zhao wrote:
> 
> 
> On 2016/1/29 22:24, Igor Mammedov wrote:
> >in current impl. condition
> >
> >build_madt() {
> >   ...
> >   if (test_bit(i, cpuinfo->found_cpus))
> >
> >is always true since loop handles only present CPUs
> >in range [0..smp_cpus).
> >But to fill usless cpuinfo->found_cpus we do unnecessary
> >scan over QOM tree to find the same CPUs.
> >So mark GICC as present always and drop not needed
> >code that fills cpuinfo->found_cpus.
> >
> >Signed-off-by: Igor Mammedov<address@hidden>
> >---
> >It's just simple cleanup but I'm trying to generalize
> >a bit CPU related ACPI tables and as part of it get rid
> >of found_cpus bitmap and if possible cpu_index usage
> >in ACPI parts of code.
> >---
> >  hw/arm/virt-acpi-build.c | 26 +++-----------------------
> >  1 file changed, 3 insertions(+), 23 deletions(-)
> >
> >diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c
> >index 87fbe7c..3ed39fc 100644
> >--- a/hw/arm/virt-acpi-build.c
> >+++ b/hw/arm/virt-acpi-build.c
> >@@ -46,20 +46,6 @@
> >  #define ARM_SPI_BASE 32
> >  #define ACPI_POWER_BUTTON_DEVICE "PWRB"
> >
> >-typedef struct VirtAcpiCpuInfo {
> >-    DECLARE_BITMAP(found_cpus, VIRT_ACPI_CPU_ID_LIMIT);
> >-} VirtAcpiCpuInfo;
> >-
> >-static void virt_acpi_get_cpu_info(VirtAcpiCpuInfo *cpuinfo)
> >-{
> >-    CPUState *cpu;
> >-
> >-    memset(cpuinfo->found_cpus, 0, sizeof cpuinfo->found_cpus);
> >-    CPU_FOREACH(cpu) {
> >-        set_bit(cpu->cpu_index, cpuinfo->found_cpus);
> >-    }
> >-}
> >-
> >  static void acpi_dsdt_add_cpus(Aml *scope, int smp_cpus)
> >  {
> >      uint16_t i;
> >@@ -458,8 +444,7 @@ build_gtdt(GArray *table_data, GArray *linker)
> >
> >  /* MADT */
> >  static void
> >-build_madt(GArray *table_data, GArray *linker, VirtGuestInfo *guest_info,
> >-           VirtAcpiCpuInfo *cpuinfo)
> >+build_madt(GArray *table_data, GArray *linker, VirtGuestInfo *guest_info)
> >  {
> >      int madt_start = table_data->len;
> >      const MemMapEntry *memmap = guest_info->memmap;
> >@@ -489,9 +474,7 @@ build_madt(GArray *table_data, GArray *linker, 
> >VirtGuestInfo *guest_info,
> >          gicc->cpu_interface_number = i;
> >          gicc->arm_mpidr = armcpu->mp_affinity;
> >          gicc->uid = i;
> >-        if (test_bit(i, cpuinfo->found_cpus)) {
> >-            gicc->flags = cpu_to_le32(ACPI_GICC_ENABLED);
> >-        }
> >+        gicc->flags = cpu_to_le32(ACPI_GICC_ENABLED);
> >      }
> Ah, yes, it uses smp_cpus not max_cpus. But we still needs to support
> max_cpus usage even though it doesn't support vcpu hotplug currently. So we
> may need to introduce guest_info->max_cpus and use it here.

We should leave that for when the hotplug patches come, and we should
probably leave the hotplug patches until we see what Igor plans for
sharing more ACPI code between x86 and ARM.

> And below check in virt.c is not right while it should compare the global
> max_cpus with the max_cpus GIC supports.
> 
>     if (smp_cpus > max_cpus) {
>         error_report("Number of SMP CPUs requested (%d) exceeds max CPUs "
>                      "supported by machine 'mach-virt' (%d)",
>                      smp_cpus, max_cpus);
>         exit(1);
>     }

max_cpus is getting set to the number the gic supports just above this
check. So max_cpus == gic_supported_cpus already, and this check is just
confirming the number of cpus the user has selected is OK.

drew