From: Roger Larsson <roger.larsson@norran•net>
To: linuxppc-embedded@ozlabs•org
Subject: floating point in kernel (Re: insmod problem)
Date: Sat, 14 May 2005 04:55:29 +0200 [thread overview]
Message-ID: <200505140455.29179.roger.larsson@norran.net> (raw)
In-Reply-To: <ed43f07150d50a594be2bc2589e902a0@freescale.com>
On Friday 13 May 2005 15.46, Kumar Gala wrote:
> On May 13, 2005, at 8:14 AM, Mark Chambers wrote:
> > > You're using floating arithmetic in the kernel.
> > >
> > > That's not supported.
> > >
> > > Regards
> > >
> > > Pantelis
> >
> > Just for my edification:=A0 Is floating point itself not supported
> > (floating
> > point register
> > corruption or something like that) or just linking to user space
> > libraries?
>
> Use of floating point registers and instructions. Its possible to use
> FP in rare cases inside the kernel buts its extremely discouraged.
>
The kernel is doing lazy saving of FP registers, only saving for user=20
processes that uses them. And especially avoiding to save for every
interrupt!
So if you like to use any FP (registers) in kernel you have to:
=2D disable kernel preemption (YES)
=2D save previous value
=2D do your stuff
=2D restore
=2D enable preemption
I remember a preemption bug caused by using MMX/SSE to copy
memory uncached.
/RogerL
prev parent reply other threads:[~2005-05-14 1:03 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-05-13 12:33 insmod problem Marco Schramel
2005-05-13 12:46 ` Pantelis Antoniou
2005-05-13 13:14 ` Mark Chambers
2005-05-13 13:46 ` Kumar Gala
2005-05-13 17:27 ` MPC885 - USB HCI drivers Guillaume Autran
2005-05-16 21:50 ` Kylo Ginsberg
2005-05-16 22:03 ` Wolfgang Denk
2005-05-16 22:39 ` Kylo Ginsberg
2005-05-16 22:52 ` Dan Malek
2005-05-17 8:28 ` Jonathan Masel
2005-05-16 23:27 ` Wolfgang Denk
2005-05-17 6:57 ` Mike Rapoport
2005-05-17 8:15 ` Wolfgang Denk
2005-05-17 8:07 ` Pantelis Antoniou
2005-05-17 9:58 ` Bryan O'Donoghue
2005-05-17 9:44 ` Pantelis Antoniou
2005-05-17 11:33 ` Mike Rapoport
2005-05-17 12:13 ` Guillaume Autran
2005-06-09 21:19 ` linux/drivers/net/fec_8xx/* vs. linux/arch/ppc/8xx_io/fec.c Guillaume Autran
2005-06-10 6:43 ` Pantelis Antoniou
2005-05-17 12:10 ` MPC885 - USB HCI drivers Guillaume Autran
2005-05-17 18:05 ` Kylo Ginsberg
2005-05-14 2:55 ` Roger Larsson [this message]
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