linux-kernel - Re: [PATCH V3 1/5] powerpc, perf: Add new BHRB related instructions for POWER8

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Date:	Mon, 22 Apr 2013 12:33:23 +0530
From:	Anshuman Khandual <khandual@...ux.vnet.ibm.com>
To:	Michael Neuling <mikey@...ling.org>
CC:	Michael Ellerman <michael@...erman.id.au>, linuxppc-dev@...abs.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3 1/5] powerpc, perf: Add new BHRB related instructions
 for POWER8

On 04/22/2013 08:20 AM, Michael Neuling wrote:
> Michael Ellerman <michael@...erman.id.au> wrote:
> 
>> On Mon, Apr 22, 2013 at 11:13:43AM +1000, Michael Neuling wrote:
>>> Michael Ellerman <michael@...erman.id.au> wrote:
>>>
>>>> On Thu, Apr 18, 2013 at 05:56:12PM +0530, Anshuman Khandual wrote:
>>>>> This patch adds new POWER8 instruction encoding for reading
>>>>> the BHRB buffer entries and also clearing it. Encoding for
>>>>> "clrbhrb" instruction is straight forward.
>>>>
>>>> Which is "clear branch history rolling buffer" ?
>>>>
>>>>> But "mfbhrbe"
>>>>> encoding involves reading a certain index of BHRB buffer
>>>>> into a particular GPR register.
>>>>
>>>> And "Move from branch history rolling buffer entry" ?
>>>>
>>>>> diff --git a/arch/powerpc/include/asm/ppc-opcode.h b/arch/powerpc/include/asm/ppc-opcode.h
>>>>> index 8752bc8..93ae5a1 100644
>>>>> --- a/arch/powerpc/include/asm/ppc-opcode.h
>>>>> +++ b/arch/powerpc/include/asm/ppc-opcode.h
>>>>> @@ -82,6 +82,7 @@
>>>>>  #define	__REGA0_R31	31
>>>>>  
>>>>>  /* sorted alphabetically */
>>>>> +#define PPC_INST_BHRBE			0x7c00025c
>>>>
>>>> I don't think you really need this, just use the literal value below.
>>>
>>> The rest of the defines in this file do this, so Anshuman's right. 
>>
>> I don't see the point, but sure let's be consistent. Though in that case
>> he should do the same for PPC_CLRBHRB below.
> 
> Agreed.
> 

Sure, would define a new macro (PPC_INST_CLRBHRB) to encode 0x7c00035c
before using it for PPC_CLRBHRB.

> Mikey
> 
>>
>>>>> @@ -297,6 +298,12 @@
>>>>>  #define PPC_NAP			stringify_in_c(.long PPC_INST_NAP)
>>>>>  #define PPC_SLEEP		stringify_in_c(.long PPC_INST_SLEEP)
>>>>>  
>>>>> +/* BHRB instructions */
>>>>> +#define PPC_CLRBHRB		stringify_in_c(.long 0x7c00035c)
>>>>> +#define PPC_MFBHRBE(r, n)	stringify_in_c(.long PPC_INST_BHRBE | \
>>>>> +						__PPC_RS(r) | \
>>>>> +							(((n) & 0x1f) << 11))
>>>>
>>>> Why are you not using ___PPC_RB(n) here ?
>>>
>>> Actually, this is wrong.  The number field should be 10 bits (0x3ff),
>>> not 5 (0x1f)  Anshuman please fix.
>>
>> ACK.

I got it wrong, thought this as 32 instead of 1024. Would fix it.

Regards
Anshuman

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