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Re: [PATCH 0/4] target/ppc: Use probe_access

From: Richard Henderson
Subject: Re: [PATCH 0/4] target/ppc: Use probe_access
Date: Thu, 30 Jan 2020 08:09:39 -0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1

On 1/29/20 5:35 PM, Aleksandar Markovic wrote:
> 00:51 Čet, 30.01.2020. Richard Henderson <address@hidden
> <mailto:address@hidden>> је написао/ла:
>> The first two address the performance regression noticed
>> by Howard Spoelstra.  The last two are just something I
>> noticed at the same time.
> But, performance regression, according to Howard bisect analysis, happened
> because of the change in target-independant code, and the fix presented here 
> is
> in target-specific code. This defies basic logic and deserves clear and
> detailed explanation.
> My additional concern, of course, is: Are other targets exposed to performance
> degradation, and why?

Potentially, yes.  However:

It requires lots of loads in a loop, on a hot path.  I would not have guessed
that the ppc32 Load Multiple Word (et al) was on a hot path at all, since the
instructions are deprecated.  But that's what an ancient os gets you, I suppose.


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