netdev - Re: Latency difference between fifo and pfifo

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Date:	Wed, 07 Dec 2011 22:20:57 -0500 (EST)
From:	"John A. Sullivan III" <jsullivan@...nsourcedevel.com>
To:	Stephen Hemminger <shemminger@...tta.com>
Cc:	David Laight <David.Laight@...LAB.COM>, netdev@...r.kernel.org,
	Rick Jones <rick.jones2@...com>,
	Dave Taht <dave.taht@...il.com>,
	Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: Latency difference between fifo and pfifo_fast



----- Original Message -----
> From: "Stephen Hemminger" <shemminger@...tta.com>
> To: "John A. Sullivan III" <jsullivan@...nsourcedevel.com>
> Cc: "David Laight" <David.Laight@...LAB.COM>, netdev@...r.kernel.org, "Rick Jones" <rick.jones2@...com>, "Dave Taht"
> <dave.taht@...il.com>, "Eric Dumazet" <eric.dumazet@...il.com>
> Sent: Wednesday, December 7, 2011 6:49:07 PM
> Subject: Re: Latency difference between fifo and pfifo_fast
> 
> =
> > > Is this a shared network? TOS won't matter if it is only your
> > > traffic.
> > > 
> > > There are number of route metrics that you can tweak to that can
> > > reduce TCP slow
> > > start effects, like increasing the initial cwnd, etc.
> > > 
> > It is a private network dedicated only to SAN traffic - a couple of
> > SAN devices and some virtualization hosts - John
> 
> Therefore unless your switch is shared, playing with queueing and TOS
> won't help reduce absolute latency.
> You maybe able to prioritize one host or SAN over another though.
> 
That's why I was wondering if we should switch to fifo from pfifo_fast since there is no prioritization of one host or SAN over another.  Thanks - John
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