From: Gabriel Paubert <paubert@iram•es>
To: Benjamin Herrenschmidt <benh@kernel•crashing.org>
Cc: malc <av1474@comtv•ru>,
linuxppc-dev@lists•ozlabs.org, hollis@penguinppc•org
Subject: Re: Probing for native availability of isel from userspace
Date: Mon, 24 Sep 2012 10:06:33 +0200 [thread overview]
Message-ID: <20120924080633.GA8127@visitor2.iram.es> (raw)
In-Reply-To: <1348473517.1132.87.camel@pasglop>
On Mon, Sep 24, 2012 at 05:58:37PM +1000, Benjamin Herrenschmidt wrote:
> On Mon, 2012-09-24 at 09:55 +0200, Gabriel Paubert wrote:
> > On Sun, Sep 23, 2012 at 03:46:06AM +0200, Segher Boessenkool wrote:
> > > Why does the kernel emulate this, btw? I can see emulation is useful
> > > for running older binaries, for instructions that have been removed
> > > from the architecture; but for newly added instructions, or optional
> > > instructions, it hurts more than it helps?
> >
> > Indeed. I also don't understand why mfpvr is emulated. That's the kind
> > of information that should be passed to the executables through auxiliary
> > vectors. After all, you can (or could at least) compile a kernel without
> > Altivec support and run it on a processor with Altivec.
> >
> > Therefore, whether Altivec is supported or not, is a matter of
> > processor and kernel options. Provide this information through
> > the auxiliary vector and the problem is solved.
>
> Which we do. mfpvr is available as a fallback (essentially because if we
> don't do it somebody's going to parse /proc/cpuinfo which is arguably
> worse :-)
Fine. But I believe that mfpvr emulation came first, which is the point
I object to (see the mess that the fact that CPUID is available to
applications made to x86 when SSE registers were added).
Bottom line, the mappin between PVR and capabilities offered to
applications should happen in one place, and this place is the kernel.
>
> We should definitely advertise the availability of isel.
Agreed.
Cheers,
Gabriel
next prev parent reply other threads:[~2012-09-24 8:06 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-21 20:05 Probing for native availability of isel from userspace malc
2012-09-22 7:26 ` Segher Boessenkool
2012-09-22 10:12 ` malc
2012-09-22 10:21 ` Gabriel Paubert
2012-09-22 15:37 ` malc
2012-09-22 16:13 ` David Gibson
2012-09-22 19:08 ` Segher Boessenkool
2012-09-22 19:55 ` Benjamin Herrenschmidt
2012-09-22 20:17 ` malc
2012-09-23 1:46 ` Segher Boessenkool
2012-09-24 7:55 ` Gabriel Paubert
2012-09-24 7:58 ` Benjamin Herrenschmidt
2012-09-24 8:06 ` Gabriel Paubert [this message]
2012-09-24 9:41 ` Benjamin Herrenschmidt
2012-09-25 13:17 ` Segher Boessenkool
2012-09-25 20:59 ` Benjamin Herrenschmidt
2012-09-26 0:17 ` Kumar Gala
2012-09-24 23:55 ` Scott Wood
2012-09-25 0:32 ` Benjamin Herrenschmidt
2012-09-25 0:40 ` Scott Wood
2012-09-25 0:47 ` malc
2012-09-25 0:50 ` Scott Wood
2012-09-25 13:31 ` Segher Boessenkool
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