netdev - Re: [PATCH] tg3: Use static inlines not macros

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Date:	Wed, 14 May 2014 22:24:11 -0700
From:	Alexei Starovoitov <alexei.starovoitov@...il.com>
To:	Joe Perches <joe@...ches.com>
Cc:	Nithin Nayak Sujir <nsujir@...adcom.com>,
	Michael Chan <mchan@...adcom.com>,
	Veaceslav Falico <vfalico@...il.com>,
	David Laight <David.Laight@...lab.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Jay Vosburgh <j.vosburgh@...il.com>,
	Andy Gospodarek <andy@...yhouse.net>,
	Veaceslav Falico <vfalico@...hat.com>
Subject: Re: [PATCH] tg3: Use static inlines not macros

On Wed, May 14, 2014 at 5:04 PM, Joe Perches <joe@...ches.com> wrote:
> Newer versions of gcc produce better code
> so convert some macros to static inlines.
>
> $ gcc --version
> gcc (Ubuntu 4.8.2-19ubuntu1) 4.8.2
> Copyright (C) 2013 Free Software Foundation, Inc.
> This is free software; see the source for copying conditions.  There is NO
> warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
>
> (x86/defconfig)
>
> $ size drivers/net/ethernet/broadcom/tg3.o.*
>    text    data     bss     dec     hex filename
>  134282     963       0  135245   2104d drivers/net/ethernet/broadcom/tg3.o.new
>  134613     963       0  135576   21198 drivers/net/ethernet/broadcom/tg3.o.old
>
> Signed-off-by: Joe Perches <joe@...ches.com>
> ---
> On Wed, 2014-05-14 at 16:37 -0700, Alexei Starovoitov wrote:
>> On Wed, May 14, 2014 at 3:03 PM, Joe Perches <joe@...ches.com> wrote:
>> > On Wed, 2014-05-14 at 14:52 -0700, Alexei Starovoitov wrote:
>> >> I cannot imagine the case where macro would be faster than static inline
>> >> unless it wasn't inlined.
>> >
>> > For an example, look at commit 4153577a8d
>> > ("tg3: Use different macros for pci_chip_rev_id accesses")
>> >
>> > Converting these macros to static inline produces
>> > larger/slower code.  (at least with gcc 4.7.3)
>> >
>> > +#define tg3_chip_rev_id(tp)                                    \
>> > +       ((tp)->pci_chip_rev_id)
>> > +#define tg3_asic_rev(tp)                                       \
>> > +       ((tp)->pci_chip_rev_id >> 12)
>> > +#define tg3_chip_rev(tp)                                       \
>> > +       ((tp)->pci_chip_rev_id >> 8)
>> >
>>
>> hmm. interesting.
>> Using gcc 4.7.2 object file size is larger with 'static inline'
>> 2893016 vs 2868112
>> but that's due to larger debug info.
>> .text is actually smaller 000207c4 vs 00020824
>> and these three calls were inlined (even without __always_inline),
>> so I suspect it's better optimized..
>> though better optimized can very well mean slower.
>
> Compiler optimizers change with every version too.

Nice. Would interesting to hear whether performance stayed the same or not.

>  drivers/net/ethernet/broadcom/tg3.h | 20 ++++++++++++++------
>  1 file changed, 14 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/net/ethernet/broadcom/tg3.h b/drivers/net/ethernet/broadcom/tg3.h
> index 461acca..3d0cf6b 100644
> --- a/drivers/net/ethernet/broadcom/tg3.h
> +++ b/drivers/net/ethernet/broadcom/tg3.h
> @@ -3416,11 +3416,19 @@ struct tg3 {
>   *     Using statement expression macros to check tp with
>   *     typecheck(struct tg3 *, tp) also creates larger objects.
>   */

nit: the comment above needs updating.

> -#define tg3_chip_rev_id(tp)                                    \
> -       ((tp)->pci_chip_rev_id)
> -#define tg3_asic_rev(tp)                                       \
> -       ((tp)->pci_chip_rev_id >> 12)
> -#define tg3_chip_rev(tp)                                       \
> -       ((tp)->pci_chip_rev_id >> 8)
> +static inline u32 tg3_chip_rev_id(const struct tg3 *tp)
> +{
> +       return tp->pci_chip_rev_id;
> +}
> +
> +static inline u32 tg3_asic_rev(const struct tg3 *tp)
> +{
> +       return tp->pci_chip_rev_id >> 12;
> +}
> +
> +static inline u32 tg3_chip_rev(const struct tg3 *tp)
> +{
> +       return tp->pci_chip_rev_id >> 8;
> +}
>
>  #endif /* !(_T3_H) */
>
>
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