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Date:	Wed, 15 Nov 2006 01:08:41 +0200 (IST)
From:	eli@....mellanox.co.il
To:	"Stephen Hemminger" <shemminger@...l.org>
Cc:	eli@....mellanox.co.il, linux-kernel@...r.kernel.org,
	linux-net@...r.kernel.org
Subject: Re: UDP packets loss

Thanks for the commets.
I actually use UDP because I am seeking for ways to improve the
performance of IPOIB and I wanted to avoid TCP's flow control. I am really
up to making anaysis. Can you tell me more about irqbalnced? Where can I
find more info how to control it? I would like my interrupts serviced by
all CPUs in a somehow equal manner. I mentioned MSIX - the driver already
make use of MSIX and I thought this is relevant to interrupts affinity.

> 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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