linux-kernel - Re: FP in kernelspace

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Message-ID: <p733bcj3sn1.fsf@verdi.suse.de>
Date:	30 Jul 2006 19:32:50 +0200
From:	Andi Kleen <ak@...e.de>
To:	Jiri Slaby <jirislaby@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: FP in kernelspace

Jiri Slaby <jirislaby@...il.com> writes:

> I have a driver written for 2.4 + RT patches with FP support. I want
> it to work in 2.6. How to implement FP? Has anybody developped some
> "protocol" between KS and US yet? If not, could somebody point me, how
> to do it the best -- with low latency.
> The device doesn't generate irqs 

Doesn't sound like something that should be supported for mainline
then.

> So 2 questions are:
> 1) howto FP in kernel

You can use kernel_fpu_begin()/_end() around the FP code in the
kernel, but the real time people will probably hate you for it because
it disables preemption.

> 3) any way to have faster ticks (up to 5000Hz)?

There are plenty of interval timers in various hardware in a typical
system that can be used.  e.g. RTC is a common choice. Drawback is
that you might conflict with other users, especially in user space.

But please don't try to submit such a hack.

-Andi
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