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Date: Thu, 3 Nov 2016 14:16:19 +0800
From: Fam Zheng <famz@redhat.com>
Message-ID: <20161103061619.GB8860@lemon>
References: <1478103841-8686-1-git-send-email-pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH for-2.8?] rules.mak: speedup save-vars
 load-vars
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: qemu-devel@nongnu.org

On Wed, 11/02 17:24, Paolo Bonzini wrote:
> Unnesting variables spends a lot of time parsing and executing foreach
> and if functions.  Because actually very few variables have to be
> saved and restored, a good strategy is to remember what has to be done
> in load-vars, and only iterate the right variables in load-vars.
> For save-vars, unroll the foreach loop to provide another small
> improvement.
> 
> This speeds up a "noop" build from around 15.5 seconds on my laptop
> to 11.7 (25% roughly).
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
> 	I'm wondering if this would be acceptable for 2.8.

I think that's fine if you don't want to bear the slowness in 2.8. But TBH I
haven't really noticed this as an issue myself. Anyway,

Reviewed-by: Fam Zheng <famz@redhat.com>

> 	I also have sent patches to GNU make that save another
> 	20%, down to 9.8 seconds.

Wow, is there a link to the patch?

Thanks,
Fam