linux-kernel - Re: [patch 00/24] perfmon3: introduction

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Date:	Tue, 11 Nov 2008 01:29:28 +0100
From:	"stephane eranian" <eranian@...glemail.com>
To:	"Paul Mackerras" <paulus@...ba.org>
Cc:	linux-kernel@...r.kernel.org,
	"Stephen Rothwell" <sfr@...b.auug.org.au>
Subject: Re: [patch 00/24] perfmon3: introduction

Stephen,

I have updated the linux-next tree to fix the issue brought up
by Paul.

Please pull from linux-next tree.

Thanks.


On Mon, Nov 10, 2008 at 4:24 PM, stephane eranian
<eranian@...glemail.com> wrote:
> Paul,
>
> On Mon, Nov 10, 2008 at 3:41 AM, Paul Mackerras <paulus@...ba.org> wrote:
>> Stephane,
>>
>> I have just looked through this set of patches and it mostly looks
>> fine to me.  There is just one thing, and that is that the way you
>> access bitmaps using cast_ulp() won't work on 32-bit big-endian
>> machines such as 32-bit PowerPC.  I suggest that instead of using
>> cast_ulp(), you have a set of abstracted bit-vector operations that
>> can be implemented by the arch code - and on x86/ia64, they would be
>> implemented with cast_ulp() + test_bit/__set_bit/etc. as at present.
>>
>
> Thanks for bringing this up. I think we had talked about this a while back.
>
> There is indeed a problem on big endian 32-bit machines The cast will
> pick up the wrong half of the u64. I think the best solution to this problem
> is as you suggested. Consequently, I have added a perfmon abstraction (bv)
> with its set of arch callbacks. The API takes u64 *.On x86, IA-64, it simply
> calls the bitmap_*() API. On PPC, it will have to adjust when compiling for
> 32 bits.
>
> Here is the example of __set_bit() on x86:
>
> static inline void pfm_arch_bv_set_bit(int b, u64 *a)
> {
>        __set_bit(b, (unsigned long *)a);
> }
>
>
> I will push this into my linux-next tree and ask Stephen to pull from it again.
>
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