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Re: _High_ CPU usage while routing (mostly) small UDP packets

To: Karsten Desler <kdesler@xxxxxxxxxx>
Subject: Re: _High_ CPU usage while routing (mostly) small UDP packets
From: Willy Tarreau <willy@xxxxxxxxx>
Date: Wed, 8 Dec 2004 06:39:53 +0100
Cc: P@xxxxxxxxxxxxxx, "David S. Miller" <davem@xxxxxxxxxxxxx>, netdev@xxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx
In-reply-to: <20041207112139.GA3610@xxxxxxxxxx>
References: <20041206205305.GA11970@xxxxxxxxxx> <20041206134849.498bfc93.davem@xxxxxxxxxxxxx> <20041206224107.GA8529@xxxxxxxxxx> <41B58A58.8010007@xxxxxxxxxxxxxx> <20041207112139.GA3610@xxxxxxxxxx>
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On Tue, Dec 07, 2004 at 12:21:39PM +0100, Karsten Desler wrote:
 
> > I also notice that a lot of time is spent allocating
> > and freeing the packet buffers (and possible hidden
> > time due to cache misses due to allocating on one
> > CPU and freeing on another?).
> > How many [RT]xDescriptors do you have configured by the way?
> 
> 256. I increased them to 1024 shortly after the profiling run, but
> didn't notice any change in the cpu usage (will try again with cyclesoak).

Have you checked the interrupts rate ? I had an e1000 eating many CPU cycles
because it would generate 50000 interrupts/s. Passing the module
InterruptThrottleRate=5000 definitely calmed it down, and more than doubled
the data rate.

Regards
Willy


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