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authorDavid Gibson <david@gibson.dropbear.id.au>2018-01-15 16:40:23 +1100
committerDavid Gibson <david@gibson.dropbear.id.au>2018-01-17 09:35:24 +1100
commitabbc124753896f72e3715813ea20dd1924202ff0 (patch)
tree19068e4bd8f9f2ab9ab16368659681eec4cfc196 /target/ppc/compat.c
parent03ee51d3548f5f553a3089f466483c1c6d5c666b (diff)
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target/ppc: Clarify compat mode max_threads value
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>
Diffstat (limited to 'target/ppc/compat.c')
-rw-r--r--target/ppc/compat.c25
1 files changed, 17 insertions, 8 deletions
diff --git a/target/ppc/compat.c b/target/ppc/compat.c
index 276b5b5..807c906 100644
--- a/target/ppc/compat.c
+++ b/target/ppc/compat.c
@@ -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;