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Re: [Qemu-devel] [PATCH for-1.5 0/9] Disable expensive QOM cast debuggin
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH for-1.5 0/9] Disable expensive QOM cast debugging for official releases |
Date: |
Fri, 10 May 2013 15:08:00 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130311 Thunderbird/17.0.4 |
Il 10/05/2013 15:01, Anthony Liguori ha scritto:
> Paolo Bonzini <address@hidden> writes:
>
>> Cast debugging can have a substantial cost (20% or more, measured by
>> Aurelien on qemu-system-ppc64).
>
> [Needs citation]
Sure: http://permalink.gmane.org/gmane.comp.emulators.qemu/210830
49,73% perf-10672.map [.] 0x7f7853ab4e0f
13,23% qemu-system-ppc64 [.] cpu_ppc_exec
13,16% libglib-2.0.so.0.3200.4 [.] g_hash_table_lookup
8,18% libglib-2.0.so.0.3200.4 [.] g_str_hash
2,47% qemu-system-ppc64 [.] object_class_dynamic_cast
1,97% qemu-system-ppc64 [.] type_is_ancestor
1,05% libglib-2.0.so.0.3200.4 [.] g_str_equal
That's ~27%.
>> Instead of adding special-cased "fast
>> casts" in the hot paths, we can just disable it in releases. At the
>> same time, add tracing facilities that simplify the analysys of those
>> problems that cast debugging would reveal.
>
> I'd prefer not to disable but instead focus on improving performance.
For 1.5? This is a regression in 1.5 due to more and more usage of
foo_env_on_cpu.
Paolo
> I suspect any performance overhead is resolving the type string to
> typeimpl. One work around is to have a dynamic cast that takes a
> typeimpl and then use a function that returns a static similar to how
> glib works.
>
> If you've got a reproducible case where the overhead is high, it should
> be easy to check.
>
> Regards,
>
> Anthony Liguori
>
>>
>> At least patches 1-7 are for 1.5.
>>
>> Paolo Bonzini (9):
>> qom: improve documentation of cast functions
>> qom: allow casting of a NULL class
>> qom: add a fast path to object_class_dynamic_cast
>> qom: pass file/line/function to asserting casts
>> qom: trace asserting casts
>> qom: allow turning cast debugging off
>> build: disable QOM cast debugging for official releases
>> qom: simplify object_class_dynamic_cast, part 1
>> qom: simplify object_class_dynamic_cast, part 2
>>
>> configure | 20 ++++++++------
>> include/qom/object.h | 40 ++++++++++++++++++++++-----
>> qom/object.c | 77
>> ++++++++++++++++++++++++++++++++++------------------
>> trace-events | 3 ++
>> 4 files changed, 99 insertions(+), 41 deletions(-)
>>
>> --
>> 1.8.1.4
>
- [Qemu-devel] [PATCH for-1.5 2/9] qom: allow casting of a NULL class, (continued)
- [Qemu-devel] [PATCH for-1.5 2/9] qom: allow casting of a NULL class, Paolo Bonzini, 2013/05/10
- [Qemu-devel] [PATCH for-1.5 3/9] qom: add a fast path to object_class_dynamic_cast, Paolo Bonzini, 2013/05/10
- [Qemu-devel] [PATCH for-1.5 4/9] qom: pass file/line/function to asserting casts, Paolo Bonzini, 2013/05/10
- [Qemu-devel] [PATCH for-1.5 5/9] qom: trace asserting casts, Paolo Bonzini, 2013/05/10
- [Qemu-devel] [PATCH for-1.5 7/9] build: disable QOM cast debugging for official releases, Paolo Bonzini, 2013/05/10
- [Qemu-devel] [PATCH for-1.5 6/9] qom: allow turning cast debugging off, Paolo Bonzini, 2013/05/10
- [Qemu-devel] [PATCH for-1.5 8/9] qom: simplify object_class_dynamic_cast, part 1, Paolo Bonzini, 2013/05/10
- [Qemu-devel] [PATCH for-1.5 9/9] qom: simplify object_class_dynamic_cast, part 2, Paolo Bonzini, 2013/05/10
- Re: [Qemu-devel] [PATCH for-1.5 0/9] Disable expensive QOM cast debugging for official releases, Anthony Liguori, 2013/05/10
- Re: [Qemu-devel] [PATCH for-1.5 0/9] Disable expensive QOM cast debugging for official releases,
Paolo Bonzini <=
- Re: [Qemu-devel] [PATCH for-1.5 0/9] Disable expensive QOM cast debugging for official releases, Andreas Färber, 2013/05/10
- Re: [Qemu-devel] [PATCH for-1.5 0/9] Disable expensive QOM cast debugging for official releases, Paolo Bonzini, 2013/05/10
- Re: [Qemu-devel] [PATCH for-1.5 0/9] Disable expensive QOM cast debugging for official releases, Aurelien Jarno, 2013/05/10
- Re: [Qemu-devel] [PATCH for-1.5 0/9] Disable expensive QOM cast debugging for official releases, Anthony Liguori, 2013/05/10
- Re: [Qemu-devel] [PATCH for-1.5 0/9] Disable expensive QOM cast debugging for official releases, Paolo Bonzini, 2013/05/10
- Re: [Qemu-devel] [PATCH for-1.5 0/9] Disable expensive QOM cast debugging for official releases, Anthony Liguori, 2013/05/10
- Re: [Qemu-devel] [PATCH for-1.5 0/9] Disable expensive QOM cast debugging for official releases, Aurelien Jarno, 2013/05/10
- Re: [Qemu-devel] [PATCH for-1.5 0/9] Disable expensive QOM cast debugging for official releases, Anthony Liguori, 2013/05/10
- Re: [Qemu-devel] [PATCH for-1.5 0/9] Disable expensive QOM cast debugging for official releases, Paolo Bonzini, 2013/05/10
- Re: [Qemu-devel] [PATCH for-1.5 0/9] Disable expensive QOM cast debugging for official releases, Anthony Liguori, 2013/05/10