linux-kernel - Re: UDP packets loss

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Message-ID: <20061114143531.2ee7eae0@freekitty>
Date:	Tue, 14 Nov 2006 14:35:31 -0800
From:	Stephen Hemminger <shemminger@...l.org>
To:	eli@....mellanox.co.il
Cc:	linux-kernel@...r.kernel.org, linux-net@...r.kernel.org
Subject: Re: UDP packets loss

On Wed, 15 Nov 2006 00:15:47 +0200 (IST)
eli@....mellanox.co.il wrote:

> Hi,
> I am running a client/server test app over IPOIB in which the client sends
> a certain amount of data to the server. When the transmittion ends, the
> server prints the bandwidth and how much data it received. I can see that
> the server reports it received about 60% that the client sent. However,
> when I look at the server's interface counters before and after the
> transmittion, I see that it actually received all the data that the client
> sent. This leads me to suspect that the networking layer somehow dropped
> some of the data. One thing to not - the CPU is 100% busy at the receiver.
> Could this be the reason (the machine I am using is 2 dual cores - 4
> CPUs).

If receiver application can't keep up UDP drops packets. The counter
receive buffer errors (UDP_MIB_RCVBUFERRORS) is incremented.

Don't expect flow control or reliable delivery; it's a datagram service!

> The secod question is how do I make the interrupts be srviced by all CPUs?
> I tried through the procfs as described by IRQ-affinity.txt but I can set
> the mask to 0F bu then I read back and see it is indeed 0f but after a few
> seconds I see it back to 02 (which means only CPU1).

Most likely, the user level irq balance daemon (irqbalanced) is adjusting it?

> 
> One more thing - the device I am using is capable of generating MSIX
> interrupts.
> 

Look at device capabilities with:

	lspci -vv


-- 
Stephen Hemminger <shemminger@...l.org>
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