netdev - Re: [PATCH net-next 2/3] bnx2x: enlarge minimal alignemnt of data offset

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Message-ID: <1403808469.28643.3.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Thu, 26 Jun 2014 11:47:49 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Yuval Mintz <Yuval.Mintz@...gic.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org,
	Ariel.Elior@...gic.com, Dmitry Kravkov <Dmitry.Kravkov@...gic.com>
Subject: Re: [PATCH net-next 2/3] bnx2x: enlarge minimal alignemnt of data
 offset

On Thu, 2014-06-26 at 14:31 +0300, Yuval Mintz wrote:
> From: Dmitry Kravkov <Dmitry.Kravkov@...gic.com>
> 
> This improves the performance of driver on machine with L1_CACHE_SHIFT of at
> most 32 bytes [HW was planned for 64-byte aligned fastpath data].
> 

>  
> -	/* Max supported alignment is 256 (8 shift) */
> -#define BNX2X_RX_ALIGN_SHIFT		min(8, L1_CACHE_SHIFT)
> +	/* Max supported alignment is 256 (8 shift)
> +	 * minimal alignment shift 6 is optimal for 57xxx HW performance
> +	 */
> +#define BNX2X_RX_ALIGN_SHIFT		max(6, min(8, L1_CACHE_SHIFT))
>  
>  	/* FW uses 2 Cache lines Alignment for start packet and size
>  	 *

I would personally use clamp(L1_CACHE_SHIFT, 6, 8)

But thats probably a matter of taste...


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