From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wei Liu Subject: Re: [PATCH net] xen-netback: fix abuse of napi budget Date: Tue, 10 Dec 2013 10:55:14 +0000 Message-ID: <20131210105514.GL32155@zion.uk.xensource.com> References: <1386670600-5882-1-git-send-email-paul.durrant@citrix.com> <1386671136.11925.46.camel@kazak.uk.xensource.com> <52A6ED35.7070003@citrix.com> <20131210103736.GJ32155@zion.uk.xensource.com> <20131210104443.GK32155@zion.uk.xensource.com> <9AAE0902D5BC7E449B7C8E4E778ABCD01ABD2E@AMSPEX01CL01.citrite.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Cc: Wei Liu , David Vrabel , Ian Campbell , "xen-devel@lists.xen.org" , "netdev@vger.kernel.org" To: Paul Durrant Return-path: Received: from smtp02.citrix.com ([66.165.176.63]:59598 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750883Ab3LJKzP (ORCPT ); Tue, 10 Dec 2013 05:55:15 -0500 Content-Disposition: inline In-Reply-To: <9AAE0902D5BC7E449B7C8E4E778ABCD01ABD2E@AMSPEX01CL01.citrite.net> Sender: netdev-owner@vger.kernel.org List-ID: On Tue, Dec 10, 2013 at 10:48:13AM +0000, Paul Durrant wrote: > > -----Original Message----- > > From: Wei Liu [mailto:wei.liu2@citrix.com] > > Sent: 10 December 2013 10:45 > > To: David Vrabel > > Cc: Ian Campbell; Paul Durrant; xen-devel@lists.xen.org; > > netdev@vger.kernel.org; Wei Liu > > Subject: Re: [PATCH net] xen-netback: fix abuse of napi budget > > > > On Tue, Dec 10, 2013 at 10:37:36AM +0000, Wei Liu wrote: > > > On Tue, Dec 10, 2013 at 10:30:13AM +0000, David Vrabel wrote: > > > > On 10/12/13 10:25, Ian Campbell wrote: > > > > > On Tue, 2013-12-10 at 10:16 +0000, Paul Durrant wrote: > > > > >> netback seemed to be somewhat confused about the napi budget > > parameter and > > > > >> basically ignored it. This patch fixes that, properly limiting the work > > done > > > > >> in each poll. > > > > > > > > > > What do you mean "ignored", xenvif_tx_submit seems to be tracking > > and > > > > > testing work_done against the budget. > > > > > > > > I have seen this warning in net_rx_action() trigger. > > > > > > > > WARN_ON_ONCE(work > weight); > > > > > > > > Which means netback wasn't limiting the work done. > > > > > > > > > > But in the original code work_done is returned by xenvif_tx_submit which > > > has guard against that situation, right? > > > > > > > And now I think I spot a bug... > > > > work_done = xenvif_tx_submit(vif, nr_gops); > > > > The second argument should really be "budget". :-( > > > > Yep - that's basically the problem. > So size-wise the attached patch is smaller. Now the only problem is that is it better to move flow control earlier. Wei. ---8<--- >>From 11db4a9cd7267a621725c48f0e0a99c1d6d31866 Mon Sep 17 00:00:00 2001 From: Wei Liu Date: Tue, 10 Dec 2013 10:49:59 +0000 Subject: [PATCH] xen-netback: correct typo nr_gops -> budget work_done should be limited by budget not nr_gops. Otherwise we trigger "WARN_ON_ONCE(work > weight)" in net/dev/core:net_rx_action. Signed-off-by: Wei Liu --- drivers/net/xen-netback/netback.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c index acf1392..b11f65d 100644 --- a/drivers/net/xen-netback/netback.c +++ b/drivers/net/xen-netback/netback.c @@ -1707,7 +1707,7 @@ int xenvif_tx_action(struct xenvif *vif, int budget) gnttab_batch_copy(vif->tx_copy_ops, nr_gops); - work_done = xenvif_tx_submit(vif, nr_gops); + work_done = xenvif_tx_submit(vif, budget); return work_done; } -- 1.7.10.4