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target/ppc: Clarify compat mode max_threads value

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We recently had some discussions that were sidetracked for a while, because
nearly everyone misapprehended the purpose of the 'max_threads' field in
the compatiblity modes table.  It's all about guest expectations, not host
expectations or support (that's handled elsewhere).

In an attempt to avoid a repeat of that confusion, rename the field to
'max_vthreads' and add an explanatory comment.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Laurent Vivier <lvivier@redhat.com>
Reviewed-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Jose Ricardo Ziviani <joserz@linux.vnet.ibm.com>
This commit is contained in:
David Gibson 2018-01-15 16:40:23 +11:00
parent 03ee51d354
commit abbc124753
3 changed files with 20 additions and 11 deletions
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4
hw/ppc/spapr.c
View file

@ -345,7 +345,7 @@ static int spapr_fixup_cpu_dt(void *fdt, sPAPRMachineState *spapr)
PowerPCCPU *cpu = POWERPC_CPU(cs);
DeviceClass *dc = DEVICE_GET_CLASS(cs);
int index = spapr_vcpu_id(cpu);
int compat_smt = MIN(smp_threads, ppc_compat_max_threads(cpu));
int compat_smt = MIN(smp_threads, ppc_compat_max_vthreads(cpu));
if ((index % smt) != 0) {
continue;
@ -503,7 +503,7 @@ static void spapr_populate_cpu_dt(CPUState *cs, void *fdt, int offset,
size_t page_sizes_prop_size;
uint32_t vcpus_per_socket = smp_threads * smp_cores;
uint32_t pft_size_prop[] = {0, cpu_to_be32(spapr->htab_shift)};
int compat_smt = MIN(smp_threads, ppc_compat_max_threads(cpu));
int compat_smt = MIN(smp_threads, ppc_compat_max_vthreads(cpu));
sPAPRDRConnector *drc;
int drc_index;
uint32_t radix_AP_encodings[PPC_PAGE_SIZES_MAX_SZ];

25
target/ppc/compat.c
View file

@ -32,7 +32,16 @@ typedef struct {
uint32_t pvr;
uint64_t pcr;
uint64_t pcr_level;
int max_threads;
/*
* Maximum allowed virtual threads per virtual core
*
* This is to stop older guests getting confused by seeing more
* threads than they think the cpu can support. Usually it's
* equal to the number of threads supported on bare metal
* hardware, but not always (see POWER9).
*/
int max_vthreads;
} CompatInfo;
static const CompatInfo compat_table[] = {
@ -45,28 +54,28 @@ static const CompatInfo compat_table[] = {
.pcr = PCR_COMPAT_3_00 | PCR_COMPAT_2_07 | PCR_COMPAT_2_06 |
PCR_COMPAT_2_05 | PCR_TM_DIS | PCR_VSX_DIS,
.pcr_level = PCR_COMPAT_2_05,
.max_threads = 2,
.max_vthreads = 2,
},
{ /* POWER7, ISA2.06 */
.name = "power7",
.pvr = CPU_POWERPC_LOGICAL_2_06,
.pcr = PCR_COMPAT_3_00 | PCR_COMPAT_2_07 | PCR_COMPAT_2_06 | PCR_TM_DIS,
.pcr_level = PCR_COMPAT_2_06,
.max_threads = 4,
.max_vthreads = 4,
},
{
.name = "power7+",
.pvr = CPU_POWERPC_LOGICAL_2_06_PLUS,
.pcr = PCR_COMPAT_3_00 | PCR_COMPAT_2_07 | PCR_COMPAT_2_06 | PCR_TM_DIS,
.pcr_level = PCR_COMPAT_2_06,
.max_threads = 4,
.max_vthreads = 4,
},
{ /* POWER8, ISA2.07 */
.name = "power8",
.pvr = CPU_POWERPC_LOGICAL_2_07,
.pcr = PCR_COMPAT_3_00 | PCR_COMPAT_2_07,
.pcr_level = PCR_COMPAT_2_07,
.max_threads = 8,
.max_vthreads = 8,
},
{ /* POWER9, ISA3.00 */
.name = "power9",
@ -80,7 +89,7 @@ static const CompatInfo compat_table[] = {
* confusing if half of the threads disappear from the guest
* if it announces it's POWER9 aware at CAS time.
*/
.max_threads = 8,
.max_vthreads = 8,
},
};
@ -192,14 +201,14 @@ void ppc_set_compat_all(uint32_t compat_pvr, Error **errp)
}
}
int ppc_compat_max_threads(PowerPCCPU *cpu)
int ppc_compat_max_vthreads(PowerPCCPU *cpu)
{
const CompatInfo *compat = compat_by_pvr(cpu->compat_pvr);
int n_threads = CPU(cpu)->nr_threads;
if (cpu->compat_pvr) {
g_assert(compat);
n_threads = MIN(n_threads, compat->max_threads);
n_threads = MIN(n_threads, compat->max_vthreads);
}
return n_threads;

2
target/ppc/cpu.h
View file

@ -1395,7 +1395,7 @@ void ppc_set_compat(PowerPCCPU *cpu, uint32_t compat_pvr, Error **errp);
#if !defined(CONFIG_USER_ONLY)
void ppc_set_compat_all(uint32_t compat_pvr, Error **errp);
#endif
int ppc_compat_max_threads(PowerPCCPU *cpu);
int ppc_compat_max_vthreads(PowerPCCPU *cpu);
void ppc_compat_add_property(Object *obj, const char *name,
uint32_t *compat_pvr, const char *basedesc,
Error **errp);