netdev - Re: sky2 stable in 2.6.12-rc1 (but still performance problem)...

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Date:	Tue, 27 Feb 2007 09:56:44 -0800
From:	Stephen Hemminger <shemminger@...ux-foundation.org>
To:	"Daniel J Blueman" <daniel.blueman@...il.com>
Cc:	"Linux Netdev" <netdev@...r.kernel.org>,
	"Linux Kernel" <linux-kernel@...r.kernel.org>,
	"Linux Networking" <linux-net@...r.kernel.org>
Subject: Re: sky2 stable in 2.6.12-rc1 (but still performance problem)...

On Tue, 27 Feb 2007 11:31:58 +0000
"Daniel J Blueman" <daniel.blueman@...il.com> wrote:

> Hi Stephen,
> 
> 2.6.21-rc1 is the first kernel where my SysKonnect Yukon 2 hardware
> with the sky2 v1.13 driver is stable under moderate load. Before a few
> GBs of data going over my GigE network quickly with NFSv4 would cause
> transmit timeouts previously, but now fine.
> 
> I am still observing a performance problem - feels like a wmb() or
> some buffer flushing is missing somewhere - disabling processor clock
> scaling reduces the problem a bit, but does not eliminate it.

That seems odd, if it was a missing barrier you would see data corruption.
Are there checksum errors?

You might be seeing hardware flow control. Look at ethtool -S eth0 output.
Previously, transmit flow control was broken

> What are your preferred way of checking performance? I think that the
> TCP send window can grow enough even if ACKs are delayed due to this
> problem, such that TCP does not immediately demonstrate this issue. I
> could restrict the window scaling factor, so it would be bound by the
> data->ACK round-trip latency, which /should/ be low, but I've been
> observing it higher. Maybe I try this.

iperf is easiest.

> I'll see what I get with iperf UDP also, since this shows min, max,
> avg UDP packet latency IIRC.
> 
> Thanks for your great work so far though!
>   Dan


-- 
Stephen Hemminger <shemminger@...ux-foundation.org>
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