netdev - Re: [PATCH] Improved network performance by balancing Rx against other work

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Message-ID: <8739ztrnrp.wl%peterc@chubb.wattle.id.au>
Date:	Mon, 22 Mar 2010 15:19:54 +1100
From:	Peter Chubb <peter.chubb@...ta.com.au>
To:	David Miller <davem@...emloft.net>
Cc:	<peter.chubb@...ta.com.au>, <netdev@...r.kernel.org>
Subject: Re: [PATCH] Improved network performance by balancing Rx against other work

>>>>> "David" == David Miller <davem@...emloft.net> writes:

David> From: Peter Chubb <peter.chubb@...ta.com.au> Date: Mon, 22 Mar
David> 2010 15:04:24 +1100

>>>>>>> "David" == David Miller <davem@...emloft.net> writes:
>>
David> From: Peter Chubb <peter.chubb@...ta.com.au> Date: Wed, 17 Mar

>> However, softIRQ processing is still not being preempted by a
>> real-time process that wakes up.

David> I thought softirqs ran as threads in the -rt kernel, why
David> doesn't preemption work properly for those threads?

I'm using the standard kernel here -- softIRQs run as threads
scheduled as SCHED_NORMAL, but because they're in the kernel, they're
not preemptible without an explicit preemption point, as far as I can
tell.  So hardware interrupts will run, and the budget/work done
mechanism will ensure that other softIRQs and in-kernel real-time
threads run, but userspace doesn't seem to get a look in.

>> I had a look at the Broadcom tg3, but it looks too hard to modify;

David> It's one of the best drivers in the locking area.

It looked good from that aspect, but used too many features of NAPI
for me to modify quickly, and still have a simple and
easy-to-understand patch.

Anyway, I'm intending to try to reproduce the results with a different
driver, as I said.

Peter C

--
Dr Peter Chubb  http://www.gelato.unsw.edu.au  peterc AT gelato.unsw.edu.au
http://www.ertos.nicta.com.au           ERTOS within National ICT Australia
--
Dr Peter Chubb  http://www.gelato.unsw.edu.au  peterc AT gelato.unsw.edu.au
http://www.ertos.nicta.com.au           ERTOS within National ICT Australia
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