From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: [PATCH net-next 3/9] sfc: Increase size of RX SKB header area Date: Tue, 16 Jul 2013 10:33:55 -0700 Message-ID: <1373996035.6097.5.camel@edumazet-glaptop> References: <1372104708.1896.29.camel@bwh-desktop.uk.level5networks.com> <1372104801.1896.32.camel@bwh-desktop.uk.level5networks.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: David Miller , netdev@vger.kernel.org, linux-net-drivers@solarflare.com To: Ben Hutchings Return-path: Received: from mail-oa0-f50.google.com ([209.85.219.50]:34925 "EHLO mail-oa0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932872Ab3GPRd6 (ORCPT ); Tue, 16 Jul 2013 13:33:58 -0400 Received: by mail-oa0-f50.google.com with SMTP id k7so1218558oag.23 for ; Tue, 16 Jul 2013 10:33:58 -0700 (PDT) In-Reply-To: <1372104801.1896.32.camel@bwh-desktop.uk.level5networks.com> Sender: netdev-owner@vger.kernel.org List-ID: On Mon, 2013-06-24 at 21:13 +0100, Ben Hutchings wrote: > From: Jon Cooper > > This allows the SKB to hold the headers without reallocation more often. > > Signed-off-by: Ben Hutchings > --- > drivers/net/ethernet/sfc/rx.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/net/ethernet/sfc/rx.c b/drivers/net/ethernet/sfc/rx.c > index b915e09..6efff3d 100644 > --- a/drivers/net/ethernet/sfc/rx.c > +++ b/drivers/net/ethernet/sfc/rx.c > @@ -36,7 +36,7 @@ > #define EFX_RECYCLE_RING_SIZE_NOIOMMU (2 * EFX_RX_PREFERRED_BATCH) > > /* Size of buffer allocated for skb header area. */ > -#define EFX_SKB_HEADERS 64u > +#define EFX_SKB_HEADERS 128u > > /* This is the percentage fill level below which new RX descriptors > * will be added to the RX descriptor ring. > This patch brings performance decrease for tunnels, because it pulls into skb->head 128 bytes worth of data. This includes TCP payload, so GRO or TCP coalescing code is less effective. Each MSS spans 2 memory areas (small part on skb->head, remaining on the fragment) : GRO packets have only 8 MSS worth of data, instead of 16. The fix would be to allocate 128 bytes in skb->head to prevent future reallocations of skb->head, but pull 64 bytes only.