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From: Bruno Piazera Larsen <>
To: Richard Henderson <>,
	Greg Kurz <>,,,,,
Subject: Re: [RFC PATCH] target/ppc: fix address translation bug for hash table mmus
Date: Tue, 8 Jun 2021 15:39:25 -0300	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

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On 08/06/2021 13:37, Bruno Piazera Larsen wrote:
> On 08/06/2021 12:35, Richard Henderson wrote:
>> On 6/8/21 7:39 AM, Bruno Piazera Larsen wrote:
>>>> That's odd.  We already have more arguments than the number of 
>>>> argument registers...  A 5x slowdown is distinctly odd.
>>> I did some more digging and the problem is not with 
>>> ppc_radix64_check_prot, the problem is ppc_radix64_xlate, which 
>>> currently has 7 arguments and we're increasing to 8. 7 feels like 
>>> the correct number, but I couldn't find docs supporting it, so I 
>>> could be wrong.
>> According to tcg/ppc/, there are 8 argument registers 
>> for ppc hosts.  But now I see you didn't actually say on which host 
>> you observed the problem...  It's 6 argument registers for x86_64 host.
> Oh, yes, sorry. I'm experiencing it in a POWER9 machine (ppc64le 
> architecture). According to tcg this shouldn't be the issue, then, so 
> idk if that's the real reason or not. All I know is that as soon as 
> gcc can't optimize an argument away it happens (fprintf in 
> radix64_xlate, using one of the mmuidx_* functions, defining those as 
> macros).
> I'll test it in my x86_64 machine and see if such a slowdown happens. 
> It's not conclusive evidence, but the function is too complex for me 
> to follow the disassembly if I can avoid it...
Test has been done: Slow down also happens on the x86_64 machine (but 
without change its already 360s, so idk if the slowdown is that 
dramatic), so it's _probably_ not going over the argument register 
count. I have no clue what could be. Still working on the struct version 
to see if anything changes.

Bruno Piazera Larsen
Instituto de Pesquisas ELDORADO 
Departamento Computação Embarcada
Analista de Software Trainee
Aviso Legal - Disclaimer <>

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      reply	other threads:[~2021-06-08 18:42 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-02 19:18 Bruno Larsen (billionai)
2021-06-02 19:26 ` Richard Henderson
2021-06-02 19:58   ` Bruno Piazera Larsen
2021-06-02 22:19     ` Richard Henderson
2021-06-07 19:29       ` Bruno Piazera Larsen
2021-06-07 21:06         ` Richard Henderson
2021-06-08 14:39           ` Bruno Piazera Larsen
2021-06-08 15:35             ` Richard Henderson
2021-06-08 16:37               ` Bruno Piazera Larsen
2021-06-08 18:39                 ` Bruno Piazera Larsen [this message]

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