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Re: [Qemu-trivial] [Qemu-devel] [PATCH] Do not enable QOM debugging by d

From: Daniel P . Berrangé
Subject: Re: [Qemu-trivial] [Qemu-devel] [PATCH] Do not enable QOM debugging by default
Date: Tue, 17 Jul 2018 10:40:13 +0100
User-agent: Mutt/1.10.0 (2018-05-17)

On Mon, Jul 16, 2018 at 09:41:12PM +0100, Peter Maydell wrote:
> On 16 July 2018 at 20:47, BALATON Zoltan <address@hidden> wrote:
> > Commit 3556c233d 5 years ago added an option to disable QOM debugging,
> > noting that it can have high performance cost but left the default to on.
> > Change the default to off and only enable it when debugging is requested
> > to avoid the performance penalty for those compiling without debug options.
> >
> > Signed-off-by: BALATON Zoltan <address@hidden>
> Looking at the code, doesn't this disable all the type checking
> on the QOM casts? That is not something I think we should drop,
> in the same way that we do not disable assert()s even in the
> non-debug build.
> Is this coming up as significant in profiling? In the past we've
> done some special casing if there are particular QOM casts in
> hot paths that use significant runtime.

There might also be scope for doing optimization of the
object_dynamic_cast_assert() implementation too.

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