Subject: Re: [PATCH net-next 2/2] gianfar: convert u64 status counters to atomic64_t

From: Claudiu Manoil <[email-masked]>
Date: Wed, 13 Feb 2013 17:22:44 +0200

On 2/13/2013 2:24 AM, Paul Gortmaker wrote:
> While looking at some asm dump for an unrelated change, Eric
> noticed in the following stats count increment code:
>
>      50b8:       81 3c 01 f8     lwz     r9,504(r28)
>      50bc:       81 5c 01 fc     lwz     r10,508(r28)
>      50c0:       31 4a 00 01     addic   r10,r10,1
>      50c4:       7d 29 01 94     addze   r9,r9
>      50c8:       91 3c 01 f8     stw     r9,504(r28)
>      50cc:       91 5c 01 fc     stw     r10,508(r28)
>
> that a 64 bit counter was used on ppc-32 without sync
> and hence the "ethtool -S" output was racy.
>
> Here we convert all the values to use atomic64_t so that
> the output will always be consistent.
>

At least it seems that this conversion results in fewer asm
instructions, as apparently addze and the double lwz/stw are
not generated anymore. Hopefully it's faster too :P

Reviewed-by: Claudiu Manoil <[email-masked]>

Thanks,
Claudiu