| Message ID | 20131210105514.GL32155@zion.uk.xensource.com |
|---|---|
| State | RFC, archived |
| Delegated to: | David Miller |
| Headers | show |
> -----Original Message----- > From: Wei Liu [mailto:wei.liu2@citrix.com] > Sent: 10 December 2013 10:55 > To: Paul Durrant > Cc: Wei Liu; David Vrabel; Ian Campbell; xen-devel@lists.xen.org; > netdev@vger.kernel.org > Subject: Re: [PATCH net] xen-netback: fix abuse of napi budget > > 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. > Yes, but I think that patch is dangerous as I explained to Ian. If we don't limit early then tx_queue can grow uncontrollably if the frontend continues to throw more data into the ring than we actually ship out on each napi poll. I will re-submit with a more elaborate description. Paul > Wei. > > ---8<--- > From 11db4a9cd7267a621725c48f0e0a99c1d6d31866 Mon Sep 17 00:00:00 > 2001 > From: Wei Liu <wei.liu2@citrix.com> > 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 <wei.liu2@citrix.com> > --- > 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 -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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; }