netdev - Re: [PATCH net-next 2/2] gianfar: convert u64 status counters to atomic64

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Message-ID: <511BAFC4.9060006@freescale.com>
Date:	Wed, 13 Feb 2013 17:22:44 +0200
From:	Claudiu Manoil <claudiu.manoil@...escale.com>
To:	Paul Gortmaker <paul.gortmaker@...driver.com>
CC:	David Miller <davem@...emloft.net>, <netdev@...r.kernel.org>,
	Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH net-next 2/2] gianfar: convert u64 status counters to
 atomic64_t

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 <claudiu.manoil@...escale.com>

Thanks,
Claudiu


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