| Message ID | 1368477106-7579-1-git-send-email-aliguori@us.ibm.com |
|---|---|
| State | New |
| Headers | show |
Il 13/05/2013 22:31, Anthony Liguori ha scritto: > This patch adds a small typename cache to ObjectClass. This allows > caching positive casts within each ObjectClass. Benchmarking a > PPC workload provided by Aurelien, this patch eliminates every > single g_hash_table_lookup() happening during the benchmark (which > was about 2 million per-second). > > With this patch applied, I get exactly the same performance (within > the margin of error) as with --disable-qom-cast-debug. > > N.B. it's safe to cache typenames only from the _assert() macros > because they are always called with string literals. Nice! Perhaps (for 1.6?) we can cache other results than class, so that interfaces are sped up as well. Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Paolo Bonzini <pbonzini@redhat.com> writes: > Il 13/05/2013 22:31, Anthony Liguori ha scritto: >> This patch adds a small typename cache to ObjectClass. This allows >> caching positive casts within each ObjectClass. Benchmarking a >> PPC workload provided by Aurelien, this patch eliminates every >> single g_hash_table_lookup() happening during the benchmark (which >> was about 2 million per-second). >> >> With this patch applied, I get exactly the same performance (within >> the margin of error) as with --disable-qom-cast-debug. >> >> N.B. it's safe to cache typenames only from the _assert() macros >> because they are always called with string literals. > > Nice! Perhaps (for 1.6?) we can cache other results than class, so that > interfaces are sped up as well. Yes, there's no reason not to store any computed data within a class. There are very few of them within QEMU and it's very easy to get to. > Reviewed-by: Paolo Bonzini <pbonzini@redhat.com> Thanks. We should leave the --disable-qom-casts present for 1.5 but I'd like to discuss reverting it for 1.6. I'll send patches once 1.6 opens up. Regards, Anthony Liguori
Il 13/05/2013 23:04, Anthony Liguori ha scritto: > We should leave the --disable-qom-casts present for 1.5 but I'd like > to discuss reverting it for 1.6. I'll send patches once 1.6 opens up. I disagree, the cost is small but still provably nonzero. We should only remove it once interfaces start to be more pervasive (it would be nice for example to replace the RTC's #ifdef TARGET_I386 with an interface). Paolo
On 13 May 2013 21:31, Anthony Liguori <aliguori@us.ibm.com> wrote: > This patch adds a small typename cache to ObjectClass. This allows > caching positive casts within each ObjectClass. Benchmarking a > PPC workload provided by Aurelien, this patch eliminates every > single g_hash_table_lookup() happening during the benchmark (which > was about 2 million per-second). That's a lot of hashtable lookups... > --- a/include/qom/object.h > +++ b/include/qom/object.h > @@ -344,6 +344,8 @@ typedef void (ObjectUnparent)(Object *obj); > */ > typedef void (ObjectFree)(void *obj); > > +#define OBJECT_CLASS_CAST_CACHE 4 Total nitpick, but shouldn't this be OBJECT_CLASS_CAST_CACHE_SIZE ? thanks -- PMM
Peter Maydell <peter.maydell@linaro.org> writes: > On 13 May 2013 21:31, Anthony Liguori <aliguori@us.ibm.com> wrote: >> This patch adds a small typename cache to ObjectClass. This allows >> caching positive casts within each ObjectClass. Benchmarking a >> PPC workload provided by Aurelien, this patch eliminates every >> single g_hash_table_lookup() happening during the benchmark (which >> was about 2 million per-second). > > That's a lot of hashtable lookups... I suspect it's due to a cast somewhere in a path checking for pending interrupts or something like that. That would get called quite often. > >> --- a/include/qom/object.h >> +++ b/include/qom/object.h >> @@ -344,6 +344,8 @@ typedef void (ObjectUnparent)(Object *obj); >> */ >> typedef void (ObjectFree)(void *obj); >> >> +#define OBJECT_CLASS_CAST_CACHE 4 > > Total nitpick, but shouldn't this be > OBJECT_CLASS_CAST_CACHE_SIZE ? Ack, I need to respin anyway so I'll make the updates. Thanks, Anthony Liguori > > thanks > -- PMM
Applied. Thanks. Regards, Anthony Liguori
diff --git a/include/qom/object.h b/include/qom/object.h index 63e2a40..23fc048 100644 --- a/include/qom/object.h +++ b/include/qom/object.h @@ -344,6 +344,8 @@ typedef void (ObjectUnparent)(Object *obj); */ typedef void (ObjectFree)(void *obj); +#define OBJECT_CLASS_CAST_CACHE 4 + /** * ObjectClass: * @@ -356,6 +358,8 @@ struct ObjectClass Type type; GSList *interfaces; + const char *cast_cache[OBJECT_CLASS_CAST_CACHE]; + ObjectUnparent *unparent; }; diff --git a/qom/object.c b/qom/object.c index f5f416b..ec88231 100644 --- a/qom/object.c +++ b/qom/object.c @@ -439,7 +439,16 @@ Object *object_dynamic_cast_assert(Object *obj, const char *typename, typename, file, line, func); #ifdef CONFIG_QOM_CAST_DEBUG - Object *inst = object_dynamic_cast(obj, typename); + int i; + Object *inst; + + for (i = 0; i < OBJECT_CLASS_CAST_CACHE; i++) { + if (obj->class->cast_cache[i] == typename) { + goto out; + } + } + + inst = object_dynamic_cast(obj, typename); if (!inst && obj) { fprintf(stderr, "%s:%d:%s: Object %p is not an instance of type %s\n", @@ -448,6 +457,15 @@ Object *object_dynamic_cast_assert(Object *obj, const char *typename, } assert(obj == inst); + + if (obj == inst) { + for (i = 1; i < OBJECT_CLASS_CAST_CACHE; i++) { + obj->class->cast_cache[i - 1] = obj->class->cast_cache[i]; + } + obj->class->cast_cache[i - 1] = typename; + } + +out: #endif return obj; } @@ -510,7 +528,16 @@ ObjectClass *object_class_dynamic_cast_assert(ObjectClass *class, trace_object_class_dynamic_cast_assert(class ? class->type->name : "(null)", typename, file, line, func); -#ifndef CONFIG_QOM_CAST_DEBUG +#ifdef CONFIG_QOM_CAST_DEBUG + int i; + + for (i = 0; i < OBJECT_CLASS_CAST_CACHE; i++) { + if (class->cast_cache[i] == typename) { + ret = class; + goto out; + } + } +#else if (!class->interfaces) { return class; } @@ -523,6 +550,15 @@ ObjectClass *object_class_dynamic_cast_assert(ObjectClass *class, abort(); } +#ifdef CONFIG_QOM_CAST_DEBUG + if (ret == class) { + for (i = 1; i < OBJECT_CLASS_CAST_CACHE; i++) { + class->cast_cache[i - 1] = class->cast_cache[i]; + } + class->cast_cache[i - 1] = typename; + } +out: +#endif return ret; }
This patch adds a small typename cache to ObjectClass. This allows caching positive casts within each ObjectClass. Benchmarking a PPC workload provided by Aurelien, this patch eliminates every single g_hash_table_lookup() happening during the benchmark (which was about 2 million per-second). With this patch applied, I get exactly the same performance (within the margin of error) as with --disable-qom-cast-debug. N.B. it's safe to cache typenames only from the _assert() macros because they are always called with string literals. Signed-off-by: Anthony Liguori <aliguori@us.ibm.com> --- include/qom/object.h | 4 ++++ qom/object.c | 40 ++++++++++++++++++++++++++++++++++++++-- 2 files changed, 42 insertions(+), 2 deletions(-)