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Date: Tue, 13 Nov 2001 10:47:09 +0100
From: Sebastian Heidl <heidl@zib.de>
To: "Richard B. Johnson" <root@chaos.analogic.com>
Cc: lkml <linux-kernel@vger.kernel.org>
Subject: Re: doing a callback from the kernel to userspace
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In-Reply-To: <Pine.LNX.3.95.1011112133630.7750A-100000@chaos.analogic.com>; from root@chaos.analogic.com on Mon, Nov 12, 2001 at 01:39:46PM -0500
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On Mon, Nov 12, 2001 at 01:39:46PM -0500, Richard B. Johnson wrote:
> Please check the 'standard' ways of making drivers before you hack
> together something as Linux-specific as a kernel thread. I have
I think a kernel thread is not a choice for me as I truly want to execute
userspace code. As I said before: like a signal handler.

> drivers that are interrupted 10,000 times per second, transfer
> data from hardware buffers in 20,240 byte chunks at an overall
> transfer rate of 24 megabytes per second. The task(s) waiting
> for these data sleep in poll(), then call read() when data
> starts to arrive. This is the De-facto standard way for Unix
> systems. I don't have "latency" problems.
Well I'm talking about really fast networking so every _micro_second I save is
worth it. My numbers are a bit different: Think about a Gigabit-Ethernet card
sending you about 80000 interrupts if it's in a bad mood ;-)

To give you a figure: I'm trying to get below 10 us for user to user latency.
Have a look at the benchmarks at www.myri.com.

thanks anyway ;-)
_sh_


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