netdev - Re: Latency difference between fifo and pfifo

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20111207152709.37b5798d@nehalam.linuxnetplumber.net>
Date:	Wed, 7 Dec 2011 15:27:09 -0800
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>
Subject: Re: Latency difference between fifo and pfifo_fast

 
> <grin> Sorry to have kicked up a storm! We really don't have a problem - just trying to optimize our environment.  We have been told by our SAN vendor that, because of the 4KB limit on block size in Linux file systems, iSCSI connections for Linux file services are latency bound and not bandwidth bound.  I'm not sure if I believe that based upon our traces where tag queueing seems to coalesce SCSI commands into larger blocks and we are able to achieve network saturation.  I was just wondering, since it is all the same traffic and hence no need to separate into bands, if I should change the qdisc on those connections from pfifo_fast (which I assume needs to look at the TOS bits, sort into bands, and poll the separate bands) to fifo which I assume simply dumps packets on the wire.  Thanks - John

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.
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html