netdev - Re: [Xen-devel] [PATCH RFC] tcp: Allow sk_wmem_alloc to exceed sysctl_tcp_limit_output

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Message-ID: <1429116128.7346.110.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Wed, 15 Apr 2015 09:42:08 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ian Campbell <ian.campbell@...rix.com>
Cc:	George Dunlap <George.Dunlap@...citrix.com>,
	Malcolm Crossley <malcolm.crossley@...rix.com>,
	Jonathan Davies <jonathan.davies@...rix.com>,
	Wei Liu <Wei.Liu2@...rix.com>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	netdev <netdev@...r.kernel.org>,
	James Morris <jmorris@...ei.org>,
	Patrick McHardy <kaber@...sh.net>,
	David Vrabel <david.vrabel@...rix.com>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	xen-devel <xen-devel@...ts.xenproject.org>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [Xen-devel] [PATCH RFC] tcp: Allow sk_wmem_alloc to exceed
 sysctl_tcp_limit_output_bytes

On Wed, 2015-04-15 at 15:36 +0100, Ian Campbell wrote:
> On Wed, 2015-04-15 at 15:19 +0100, George Dunlap wrote:
> > On Mon, Apr 13, 2015 at 4:03 PM, Malcolm Crossley
> [...]
> > > From a networking point of view, the backend is a switch. Is it OK to
> > > consider the packet to have been transmitted from the guest point of
> > > view once the backend is aware of the packet?
> > >
> > > This would help justify the skb_orphan() in the frontend.
> > 
> > This sounds sensible to me, particularly if virtio_net is already doing it.
> 
> I also find Malcolm's argument above pretty compelling.

Yes, and then you'll have to help the virtio ongoing effort trying to
get rid of this skb_orphan()

Basically you're adding head of line blocking, as a single flow is able
to fill your queue.


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