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Re: [Qemu-devel] [PATCH for-1.5 1/2] qom: aggressively optimize qom cast

From: Anthony Liguori
Subject: Re: [Qemu-devel] [PATCH for-1.5 1/2] qom: aggressively optimize qom casting
Date: Mon, 13 May 2013 16:04:01 -0500
User-agent: Notmuch/0.15.2+77~g661dcf8 (http://notmuchmail.org) Emacs/23.3.1 (x86_64-pc-linux-gnu)

Paolo Bonzini <address@hidden> 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 <address@hidden>

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


Anthony Liguori

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