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

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Date:	Mon, 13 May 2013 21:02:42 +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

Hi Ben,

On Mon, May 13, 2013 at 7:48 PM, Ben Hutchings
<bhutchings@...arflare.com> wrote:
> efx_start_datapath() asserts that we can fit 2 RX scatter buffers plus
> a software structure, each cache-aligned, into a single page.  Where
> L1_CACHE_BYTES == 256 and PAGE_SIZE == 4096, which is the case on
> s390, this assertion fails.  Reduce EFX_RX_USR_BUF_SIZE to make this
> work.
>
> This should also be good for performance, as it ensures that each RX
> scatter buffer covers whole cache lines and slightly reduces the use
> of DMA writes that can require a read-modify-write on inter-processor
> links.
>
> (We could use 2048 - L1_CACHE_BYTES, but EFX_RX_USR_BUF_SIZE also
> affects user-level networking where a larger amount of housekeeping
> data may be needed.  Although this version of the driver does not
> support user-level networking, I prefer to keep scattering behaviour
> consistent with the out-of-tree version.)
>
> Reported-by: Geert Uytterhoeven <geert@...ux-m68k.org>
> Reported-by: Heiko Carstens <heiko.carstens@...ibm.com>
> Signed-off-by: Ben Hutchings <bhutchings@...arflare.com>
> ---
> Heiko or Geert, please confirm that this really does fix the build

Thanks! But unfortunately I still get the same error:

  CC [M]  drivers/net/ethernet/sfc/efx.o
/scratch/geert/linux/linux-m68k/drivers/net/ethernet/sfc/efx.c: In
function 'efx_start_datapath':
/scratch/geert/linux/linux-m68k/drivers/net/ethernet/sfc/efx.c:646:3:
error: call to '__compiletime_assert_648' declared with attribute
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

> failure - I don't have an s390 toolchain.

http://kernel.org/pub/tools/crosstool/files/bin/

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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