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[PATCH 2/6] cpu: cache CPUClass in CPUState for hot code paths
From: |
Cédric Le Goater |
Subject: |
[PATCH 2/6] cpu: cache CPUClass in CPUState for hot code paths |
Date: |
Fri, 23 Sep 2022 10:47:59 +0200 |
From: Alex Bennée <alex.bennee@linaro.org>
The class cast checkers are quite expensive and always on (unlike the
dynamic case who's checks are gated by CONFIG_QOM_CAST_DEBUG). To
avoid the overhead of repeatedly checking something which should never
change we cache the CPUClass reference for use in the hot code paths.
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20220811151413.3350684-3-alex.bennee@linaro.org>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
---
include/hw/core/cpu.h | 9 +++++++++
cpu.c | 9 ++++-----
2 files changed, 13 insertions(+), 5 deletions(-)
diff --git a/include/hw/core/cpu.h b/include/hw/core/cpu.h
index 500503da1316..1a7e1a93804a 100644
--- a/include/hw/core/cpu.h
+++ b/include/hw/core/cpu.h
@@ -51,6 +51,13 @@ typedef int (*WriteCoreDumpFunction)(const void *buf, size_t
size,
*/
#define CPU(obj) ((CPUState *)(obj))
+/*
+ * The class checkers bring in CPU_GET_CLASS() which is potentially
+ * expensive given the eventual call to
+ * object_class_dynamic_cast_assert(). Because of this the CPUState
+ * has a cached value for the class in cs->cc which is set up in
+ * cpu_exec_realizefn() for use in hot code paths.
+ */
typedef struct CPUClass CPUClass;
DECLARE_CLASS_CHECKERS(CPUClass, CPU,
TYPE_CPU)
@@ -317,6 +324,8 @@ struct qemu_work_item;
struct CPUState {
/*< private >*/
DeviceState parent_obj;
+ /* cache to avoid expensive CPU_GET_CLASS */
+ CPUClass *cc;
/*< public >*/
int nr_cores;
diff --git a/cpu.c b/cpu.c
index 584ac78baf96..14365e36f3a1 100644
--- a/cpu.c
+++ b/cpu.c
@@ -131,9 +131,8 @@ const VMStateDescription vmstate_cpu_common = {
void cpu_exec_realizefn(CPUState *cpu, Error **errp)
{
-#ifndef CONFIG_USER_ONLY
- CPUClass *cc = CPU_GET_CLASS(cpu);
-#endif
+ /* cache the cpu class for the hotpath */
+ cpu->cc = CPU_GET_CLASS(cpu);
cpu_list_add(cpu);
if (!accel_cpu_realizefn(cpu, errp)) {
@@ -151,8 +150,8 @@ void cpu_exec_realizefn(CPUState *cpu, Error **errp)
if (qdev_get_vmsd(DEVICE(cpu)) == NULL) {
vmstate_register(NULL, cpu->cpu_index, &vmstate_cpu_common, cpu);
}
- if (cc->sysemu_ops->legacy_vmsd != NULL) {
- vmstate_register(NULL, cpu->cpu_index, cc->sysemu_ops->legacy_vmsd,
cpu);
+ if (cpu->cc->sysemu_ops->legacy_vmsd != NULL) {
+ vmstate_register(NULL, cpu->cpu_index,
cpu->cc->sysemu_ops->legacy_vmsd, cpu);
}
#endif /* CONFIG_USER_ONLY */
}
--
2.37.3
- [PATCH 0/6] aspeed: avocado test boosts, Cédric Le Goater, 2022/09/23
- [PATCH 6/6] aspeed/smc: Cache AspeedSMCClass, Cédric Le Goater, 2022/09/23
- [PATCH 3/6] hw/core/cpu-sysemu: used cached class in cpu_asidx_from_attrs, Cédric Le Goater, 2022/09/23
- [PATCH 1/6] tests/avocado/machine_aspeed.py: Fix typos on buildroot, Cédric Le Goater, 2022/09/23
- [PATCH 4/6] cputlb: used cached CPUClass in our hot-paths, Cédric Le Goater, 2022/09/23
- [PATCH 2/6] cpu: cache CPUClass in CPUState for hot code paths,
Cédric Le Goater <=
- [PATCH 5/6] ssi: cache SSIPeripheralClass to avoid GET_CLASS(), Cédric Le Goater, 2022/09/23