Prev: [PATCH] Warn on unnecessary spaces before quoted newlines
Next: Possible NULL pointer dereference in m32r
From: Andrew Morton on 1 Feb 2010 15:50
On Sat, 30 Jan 2010 17:45:17 +0800
Wu Fengguang <fengguang.wu(a)intel.com> wrote:

> This allows use of hweight_long() in BUILD_BUG_ON().
> Suggested by Jamie.
>
> CC: Jamie Lokier <jamie(a)shareable.org>
> CC: Roland Dreier <rdreier(a)cisco.com>
> Signed-off-by: Wu Fengguang <fengguang.wu(a)intel.com>
> ---
> include/linux/bitops.h | 12 ++++++++----
> 1 file changed, 8 insertions(+), 4 deletions(-)
>
> --- linux-mm.orig/include/linux/bitops.h 2009-07-20 20:10:19.000000000 +0800
> +++ linux-mm/include/linux/bitops.h 2010-01-30 17:41:15.000000000 +0800
> @@ -40,10 +40,14 @@ static __inline__ int get_count_order(un
> return order;
> }
>
> -static inline unsigned long hweight_long(unsigned long w)
> -{
> - return sizeof(w) == 4 ? hweight32(w) : hweight64(w);
> -}
> +#define hweight_long(x) \
> +( \
> + __builtin_constant_p(x) ? \
> + __builtin_popcountl(x) : \
> + (sizeof(x) <= 4 ? \
> + hweight32(x) : \
> + hweight64(x)) \
> +)
>
> /**
> * rol32 - rotate a 32-bit value left

Peter's been mucking with a compile-time HWEIGHT(). An outdated
version of that is presently in linux-next.

(I wonder if it could have used __builtin_popcount)

(I wonder which gcc versions support __builtin_popcount)

Anyway, I suspect you should be using that rather than tweaking
hweight_long().
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo(a)vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
From: Peter Zijlstra on 3 Feb 2010 10:20
On Wed, 2010-02-03 at 07:08 -0800, Andrew Morton wrote:
> On Wed, 3 Feb 2010 21:39:51 +0800 Wu Fengguang <fengguang.wu(a)intel.com> wrote:
>
> > Is there an official lowest GCC version that Linux supports?
>
> Documentation/Changes says gcc-3.2.

Anyway, its not like that macro I used isn't straight forward. Not much
a builtin can do better.

The only benefit the builtin has is possibly use machine popcnt
instructions but we already deal with that in the kernel.



--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo(a)vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
From: Andrew Morton on 3 Feb 2010 10:20
On Wed, 3 Feb 2010 21:39:51 +0800 Wu Fengguang <fengguang.wu(a)intel.com> wrote:

> Is there an official lowest GCC version that Linux supports?

Documentation/Changes says gcc-3.2.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo(a)vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
From: Peter Zijlstra on 3 Feb 2010 10:50
On Wed, 2010-02-03 at 07:42 -0800, Andrew Morton wrote:
> On Wed, 03 Feb 2010 16:15:57 +0100 Peter Zijlstra <peterz(a)infradead.org> wrote:
>
> > On Wed, 2010-02-03 at 07:08 -0800, Andrew Morton wrote:
> > > On Wed, 3 Feb 2010 21:39:51 +0800 Wu Fengguang <fengguang.wu(a)intel.com> wrote:
> > >
> > > > Is there an official lowest GCC version that Linux supports?
> > >
> > > Documentation/Changes says gcc-3.2.
> >
> > Anyway, its not like that macro I used isn't straight forward. Not much
> > a builtin can do better.
> >
> > The only benefit the builtin has is possibly use machine popcnt
> > instructions but we already deal with that in the kernel.
>
> We didn't deal with it on every architecture, which is something which
> the compiler extension takes care of.
>
> In fact I can't find anywhere where we dealt with it on x86.

>From what I know the popcnt ins on x86 is relatively new, hpa was going
to look at supporting it using alternatives.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo(a)vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
From: Andrew Morton on 3 Feb 2010 10:50
On Wed, 03 Feb 2010 16:15:57 +0100 Peter Zijlstra <peterz(a)infradead.org> wrote:

> On Wed, 2010-02-03 at 07:08 -0800, Andrew Morton wrote:
> > On Wed, 3 Feb 2010 21:39:51 +0800 Wu Fengguang <fengguang.wu(a)intel.com> wrote:
> >
> > > Is there an official lowest GCC version that Linux supports?
> >
> > Documentation/Changes says gcc-3.2.
>
> Anyway, its not like that macro I used isn't straight forward. Not much
> a builtin can do better.
>
> The only benefit the builtin has is possibly use machine popcnt
> instructions but we already deal with that in the kernel.

We didn't deal with it on every architecture, which is something which
the compiler extension takes care of.

In fact I can't find anywhere where we dealt with it on x86.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo(a)vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
 |  Next  |  Last
Pages: 1 2 3 4 5 6
Prev: [PATCH] Warn on unnecessary spaces before quoted newlines
Next: Possible NULL pointer dereference in m32r