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SubjectRe: [PATCH V3 1/5] powerpc, perf: Add new BHRB related instructions for POWER8
On 04/22/2013 05:11 AM, Michael Ellerman 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" ?
>

Sure, would add these descriptions in the change log.

>> 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.
>
>> @@ -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 ?
>

I would replace __PPC_RS(r) with __PPC_RT(r) which makes more sense from
instruction encoding point of view.

Regards
Anshuman



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