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

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Date:	Mon, 10 Nov 2008 16:24:10 +0100
From:	"stephane eranian" <eranian@...glemail.com>
To:	"Paul Mackerras" <paulus@...ba.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [patch 00/24] perfmon3: introduction

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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