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Re: [Qemu-devel] [PATCH for-1.5 0/9] Disable expensive QOM cast debuggin
From: |
Aurelien Jarno |
Subject: |
Re: [Qemu-devel] [PATCH for-1.5 0/9] Disable expensive QOM cast debugging for official releases |
Date: |
Fri, 10 May 2013 21:00:19 +0200 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
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?
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.
> As soon as we open up 1.6 for development, we face an immediate
> regression in performance. So we need to fix the real problem here
> anyway.
>
> I strongly suspect that if there is a problem, that optimizing
> leaf/concrete casts will take care of it. Otherwise, a small lookup
> cache ought to do the trick too. We can even use pointer comparisons
> for the lookup cache which should make it extremely cheap.
>
>
> 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 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.
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.
--
Aurelien Jarno GPG: 1024D/F1BCDB73
address@hidden http://www.aurel32.net
- Re: [Qemu-devel] [PATCH for-1.5 8/9] qom: simplify object_class_dynamic_cast, part 1, (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 <=
- 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, 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