Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932916Ab3IDVAp (ORCPT ); Wed, 4 Sep 2013 17:00:45 -0400 Received: from mail-pa0-f45.google.com ([209.85.220.45]:57013 "EHLO mail-pa0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932449Ab3IDVAn (ORCPT ); Wed, 4 Sep 2013 17:00:43 -0400 Message-ID: <1378328440.7360.124.camel@edumazet-glaptop> Subject: Re: [PATCH] net/core: Order-3 frag allocator causes SWIOTLB bouncing under Xen From: Eric Dumazet To: Zoltan Kiss Cc: Konrad Rzeszutek Wilk , "David S. Miller" , Eric Dumazet , Neil Horman , Li Zefan , Eliezer Tamir , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, malcolm.crossley@citrix.com, david.vrabel@citrix.com, xen-devel@lists.xen.org Date: Wed, 04 Sep 2013 14:00:40 -0700 In-Reply-To: <1378327638-23956-1-git-send-email-zoltan.kiss@citrix.com> References: <1378327638-23956-1-git-send-email-zoltan.kiss@citrix.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3-0ubuntu6 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1965 Lines: 49 On Wed, 2013-09-04 at 21:47 +0100, Zoltan Kiss wrote: > THIS PATCH IS NOT INTENDED TO BE UPSTREAMED, IT HAS ONLY INFORMING PURPOSES! > > I've noticed a performance regression with upstream kernels when used as Dom0 > under Xen. The classic kernel can utilize the whole bandwidth of a 10G NIC > (ca. 9.3 Gbps), but upstream can reach only ca. 7 Gbps. I found that it > happens because SWIOTLB has to do double buffering. The per task frag > allocator introduced in 5640f7 creates 32 kb frags, which are not contiguous > in mfn space. > This patch provides a workaround by going back to the old way. The possible > ideas came up to solve this: > > * make sure Dom0 memory is contiguous: it sounds trivial, but doesn't work with > driver domains, and there are lots of situations where this is not possible. > * use PVH Dom0: so we will have IOMMU. In the future sometime. > * use IOMMU with PV Dom0: this seems to happen earlier. > > Signed-off-by: Zoltan Kiss > --- > net/core/sock.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/net/core/sock.c b/net/core/sock.c > index 2c097c5..854a0ea 100644 > --- a/net/core/sock.c > +++ b/net/core/sock.c > @@ -1812,7 +1812,7 @@ struct sk_buff *sock_alloc_send_skb(struct sock *sk, unsigned long size, > EXPORT_SYMBOL(sock_alloc_send_skb); > > /* On 32bit arches, an skb frag is limited to 2^15 */ > -#define SKB_FRAG_PAGE_ORDER get_order(32768) > +#define SKB_FRAG_PAGE_ORDER get_order(4096) > Well, this hack is not new... We have dev->gso_max_size and dev->gso_max_segs We also have in net-next sk_pacing_rate and dynamic TSO sizing. Maybe you could add proper infrastructure to deal with Xen limitations. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/