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Message-ID: <20100501183544.GC27062@shisha.kicks-ass.net>
Date: Sat, 1 May 2010 21:35:44 +0300
From: Alexander Shishkin <virtuoso@...nd.org>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Imre Deak <imre.deak@...ia.com>,
Russell King - ARM Linux <linux@....linux.org.uk>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
Jamie Lokier <jamie@...reable.org>,
"rostedt@...dmis.org" <rostedt@...dmis.org>,
"mingo@...e.hu" <mingo@...e.hu>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] create generic alignment api (v5)
On Sun, Mar 28, 2010 at 08:09:00 -0400, Mathieu Desnoyers wrote:
> Rather than re-doing the "alignment on a type size" trick all over again at
> different levels, import the "ltt_align" from LTTng into kernel.h and make this
> available to everyone. Renaming to:
>
> - object_align()
> - object_align_floor()
> - offset_align()
> - offset_align_floor()
Do you plan to have this integrated to the mainline? I'd like to use one of
these in my next version of the __xchg patch. So, do you need any help or
feedback or whatnot with this one?
> Changelog since v4:
> - add missing ( ) around parameters within object_align() and
> object_align_floor().
> - More coding style cleanups to ALIGN() (checkpatch.pl is happy now).
>
> Changelog since v3:
> - optimize object_align*() so fewer instructions are needed for alignment of
> addresses known dynamically. Use the (already existing) "ALIGN()", and create
> the "ALIGN_FLOOR()" macro.
> - While we are there, let's clean up the ALIGN() macros wrt coding style. e.g.
> missing parenthesis around the first use of the "x" parameter in ALIGN().
>
> Changelog since v2:
> - Fix object_align*(): should use object size alignment, not pointer alignment.
>
> Changelog since v1:
> - Align on the object natural alignment
> (rather than min(arch word alignment, natural alignment))
>
> The advantage of separating the API in "object alignment" and "offset alignment"
> is that it gives more freedom to play with offset alignment. Very useful to
> implement a tracer ring-buffer alignment. (hint hint)
>
> Typical users will use "object alignment", but infrastructures like tracers
> which need to perform alignment of statically known base+offsets will typically
> use "offset alignment", because it allows to align with respect to a base rather
> than to pass an absolute address.
>
> We use "sizeof(object)" rather than "__alignof__()" object because alignof
> returns "recommended" object alignment for the architecture, which can be
> sub-optimal on some architectures. By ensuring alignment on the object size, we
> are sure to make the right choice.
>
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> CC: Russell King - ARM Linux <linux@....linux.org.uk>
> Cc: Alexander Shishkin <virtuoso@...nd.org>,
> CC: linux-arm-kernel@...ts.infradead.org
> CC: Imre Deak <imre.deak@...ia.com>
> CC: Jamie Lokier <jamie@...reable.org>
> CC: rostedt@...dmis.org
> CC: mingo@...e.hu
Acked-by: Alexander Shishkin <virtuoso@...nd.org>
> ---
> include/linux/kernel.h | 45 +++++++++++++++++++++++++++++++++++++++++----
> 1 file changed, 41 insertions(+), 4 deletions(-)
>
> Index: linux-2.6-lttng/include/linux/kernel.h
> ===================================================================
> --- linux-2.6-lttng.orig/include/linux/kernel.h 2010-03-27 20:46:07.000000000 -0400
> +++ linux-2.6-lttng/include/linux/kernel.h 2010-03-28 20:06:27.000000000 -0400
> @@ -37,10 +37,47 @@ extern const char linux_proc_banner[];
>
> #define STACK_MAGIC 0xdeadbeef
>
> -#define ALIGN(x,a) __ALIGN_MASK(x,(typeof(x))(a)-1)
> -#define __ALIGN_MASK(x,mask) (((x)+(mask))&~(mask))
> -#define PTR_ALIGN(p, a) ((typeof(p))ALIGN((unsigned long)(p), (a)))
> -#define IS_ALIGNED(x, a) (((x) & ((typeof(x))(a) - 1)) == 0)
> +#define ALIGN(x, a) __ALIGN_MASK((x), (typeof(x)) (a) - 1)
> +#define __ALIGN_MASK(x, mask) (((x) + (mask)) & ~(mask))
> +#define PTR_ALIGN(p, a) ((typeof(p)) ALIGN((unsigned long) (p), (a)))
> +#define ALIGN_FLOOR(x, a) __ALIGN_FLOOR_MASK((x), (typeof(x)) (a) - 1)
> +#define __ALIGN_FLOOR_MASK(x, mask) ((x) & ~(mask))
> +#define PTR_ALIGN_FLOOR(p, a) \
> + ((typeof(p)) ALIGN_FLOOR((unsigned long) (p), (a)))
> +#define IS_ALIGNED(x, a) (((x) & ((typeof(x)) (a) - 1)) == 0)
> +
> +/*
> + * Align pointer on natural object alignment. Object size must be power of two.
> + */
> +#define object_align(obj) PTR_ALIGN((obj), sizeof(*(obj)))
> +#define object_align_floor(obj) PTR_ALIGN_FLOOR((obj), sizeof(*(obj)))
> +
> +/**
> + * offset_align - Calculate the offset needed to align an object on its natural
> + * alignment towards higher addresses.
> + * @align_drift: object offset from an "alignment"-aligned address.
> + * @alignment: natural object alignment. Must be non-zero, power of 2.
> + *
> + * Returns the offset that must be added to align towards higher
> + * addresses.
> + */
> +static inline size_t offset_align(size_t align_drift, size_t alignment)
> +{
> + return (alignment - align_drift) & (alignment - 1);
> +}
> +
> +/**
> + * offset_align_floor - Calculate the offset needed to align an object
> + * on its natural alignment towards lower addresses.
> + * @align_drift: object offset from an "alignment"-aligned address.
> + * @alignment: natural object alignment. Must be non-zero, power of 2.
> + *
> + * Returns the offset that must be substracted to align towards lower addresses.
> + */
> +static inline size_t offset_align_floor(size_t align_drift, size_t alignment)
> +{
> + return (align_drift - alignment) & (alignment - 1);
> +}
>
> #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]) + __must_be_array(arr))
>
>
> --
> Mathieu Desnoyers
> Operating System Efficiency R&D Consultant
> EfficiOS Inc.
> http://www.efficios.com
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