netdev - Re: [PATCH v4 0/10] bql: Byte Queue Limits

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Date:	Tue, 29 Nov 2011 09:43:54 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Dave Taht <dave.taht@...il.com>
Cc:	John Fastabend <john.r.fastabend@...el.com>,
	Tom Herbert <therbert@...gle.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH v4 0/10] bql: Byte Queue Limits

Le mardi 29 novembre 2011 à 09:37 +0100, Dave Taht a écrit :
> On Tue, Nov 29, 2011 at 8:23 AM, John Fastabend
> <john.r.fastabend@...el.com> wrote:
> >
> > I wonder if we should consider enabling TSO/GSO per queue or per traffic
> > class on devices that support this. At least in devices that support
> > multiple traffic classes it seems to be a common usage case to put bulk
> > storage traffic (iSCSI) on a traffic class and low latency traffic on a
> > separate traffic class, VoIP for example.
> 
> 
> VOIP is a drop in the bucket.
> 
> Turning TSO off on TCP exiting the datacenter (or more specifically),
> destined anywhere there is potential tx/rx bandwidth disparity
> would be goooooood.
> 

If your cpu is fast enough (and they are most of the time), this makes
no difference at all.

Instead of consuming 3% of cpu with TSO, you'll consume 10% or 15% and
no difference seen on the wire.

Really, if you want to avoid bursts, TSO has litle to do with them.



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