linux-kernel - Re: [PATCH net] sfc: Reduce RX scatter buffer size to multiple of 256

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Date:	Mon, 13 May 2013 21:16:06 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	David Miller <davem@...emloft.net>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Solarflare linux maintainers <linux-net-drivers@...arflare.com>,
	Linux Kernel Development <linux-kernel@...r.kernel.org>,
	linux-s390@...r.kernel.org,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net] sfc: Reduce RX scatter buffer size to multiple of 256

On Mon, May 13, 2013 at 9:11 PM, Ben Hutchings
<bhutchings@...arflare.com> wrote:
>> error: BUILD_BUG_ON failed: sizeof(struct efx_rx_page_state) +
>> EFX_PAGE_IP_ALIGN + EFX_RX_USR_BUF_SIZE > PAGE_SIZE / 2
>> make[4]: *** [drivers/net/ethernet/sfc/efx.o] Error 1
>
> OK, this doesn't work because on s390 EFX_PAGE_IP_ALIGN == 2 (this macro

Yeah, that's what I just discovered, too.

#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
#define EFX_PAGE_IP_ALIGN 0
#else
#define EFX_PAGE_IP_ALIGN NET_IP_ALIGN
#endif

> is equivalent to NET_IP_ALIGN, though that wasn't always true).  So DMA
> is going to be misaligned on s390 anyway.

Hmm, so it's making the choice between misaligned CPU and misaligned
DMA? Sounds fishy...

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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