[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH for-1.5 0/9] Disable expensive QOM cast debuggin
From: |
Anthony Liguori |
Subject: |
Re: [Qemu-devel] [PATCH for-1.5 0/9] Disable expensive QOM cast debugging for official releases |
Date: |
Fri, 10 May 2013 14:35:54 -0500 |
User-agent: |
Notmuch/0.15.2+77~g661dcf8 (http://notmuchmail.org) Emacs/23.3.1 (x86_64-pc-linux-gnu) |
Aurelien Jarno <address@hidden> writes:
> On Fri, May 10, 2013 at 12:41:07PM -0500, Anthony Liguori wrote:
>> Paolo Bonzini <address@hidden> writes:
>>
>> > Il 10/05/2013 16:39, Anthony Liguori ha scritto:
>> >> I just oppose the notion of disabling casts and *especially* only
>> >> disabling casts for official builds.
>> >
>> > This actually happens all the time. Exactly this kind of type-safe cast
>> > is disabled in releases of GCC, but enabled when building from svn trunk.
>>
>> Let's assume for a moment that you are right and this behavior is what
>> we should have. Let's also assume there is a real regression here
>> which has yet to have been established.
>
> I have pointed out in another mail of this thread, that this type
> checking account for about 9% of slowdown. Isn't that enough to say it's
> a regression?
Yes, it's a regression. I hadn't seen your note when I wrote the above.
I believe http://article.gmane.org/gmane.comp.emulators.qemu/210976
fixes the problem without eliminating any checking.
> I still have to compare to 1.4, but it's not very fair, as a
> significant work has been but on TCG to improve the performances,
> especially on the target-ppc code.
>
> I am currently preparing an image so that people can test that
> themselves.
I can reproduce large numbers of casts FWIW so no need to on my end.
I've confirmed the above patch fixes it.
>> Disabling casts doesn't give us a long term fix. One of the solutions
>> above does and patches also exist.
>
> Why do you insist on using dynamic cast, on a hot path?
It's a question of safety.
> It was using a
> simple pointer before QOM in 1.4, it won't be less safe with if we use
> a static cast instead of a dynamic one in 1.5.
The patch I posted should make it equally fast.
> With your arguments, we should drop all dataplane code, as it doesn't
> use the QEMU core code. People should just not complain about the
> performance.
No one is complaining about performance.
I merely stated that if performance is a problem, give us a chance to
fix it before completely disabling a feature.
And indeed, now I have a fix that doesn't disable anything.
Regards,
Anthony Liguori
>
> --
> Aurelien Jarno GPG: 1024D/F1BCDB73
> address@hidden http://www.aurel32.net
- [Qemu-devel] [PATCH for-1.5 9/9] qom: simplify object_class_dynamic_cast, part 2, (continued)
- [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, 2013/05/10
- 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 <=
- 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, Paolo Bonzini, 2013/05/11
- Re: [Qemu-devel] [PATCH for-1.5 0/9] Disable expensive QOM cast debugging for official releases, Aurelien Jarno, 2013/05/11
- 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, Andreas Färber, 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