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List:       e1000-devel
Subject:    Re: [E1000-devel] InterruptThrottleRate for multiple adapters
From:       "Duyck, Alexander H" <alexander.h.duyck () intel ! com>
Date:       2010-04-28 16:18:32
Message-ID: 80769D7B14936844A23C0C43D9FBCF0F254F1F3960 () orsmsx501 ! amr ! corp ! intel ! com
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"Oleg A. Arkhangelsky" wrote:
> Hello,
> 
> Could you please explain this note found in README file of igb driver
> distribution? 
> 
> ---
> 
> NOTE:  When igb is loaded with default settings and multiple adapters
> are in use simultaneously, the CPU utilization may increase
> non- linearly.  In order to limit the CPU utilization without
> impacting the overall throughput, we recommend that you load
> the driver as follows:
> 
> modprobe igb InterruptThrottleRate=3000,3000,3000
> 
> ---
> 
> I don't understand why CPU utilization may increase *non-linearly* in
> this case. Is this means that default settings for dual- and
> quad-port adapters are bad when we talk 
> about CPU usage?
> 
> Thank you!

It isn't that the default settings are bad, it just means that they aren't optimized \
for a multiple adapter setup in which you are running multiple quad-port or dual-port \
adapters.  

The advantage of setting the interrupt throttle rate as suggested in the note is that \
the CPU utilization will be lower due to fewer interrupts, however the latency will \
be higher.

The default settings are meant to be the best trade-off between CPU utilization and \
latency, but they were optimized for a single adapter and not the case where you \
might have more ports in the system than CPU cores.

Thanks,

Alex
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