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cpu: cache CPUClass in CPUState for hot code paths

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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>
Message-Id: <20220923084803.498337-3-clg@kaod.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
This commit is contained in:
Alex Bennée 2022-09-23 10:47:59 +02:00 committed by Richard Henderson
parent efbf38d73e
commit 6fbdff8706
2 changed files with 13 additions and 5 deletions
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9
cpu.c
View file

@ -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 */
}

9
include/hw/core/cpu.h
View file

@ -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;