SPE & Interrupt context (was how to make use of SPE instructions)

Mon, 26 Jan 2015 21:10:20 -0800 

On Tue, 2015-01-20 at 14:53 +0000, Markus Stockhausen wrote:
> > Von: Scott Wood [scottw...@freescale.com]
> > Gesendet: Dienstag, 20. Januar 2015 08:38
> > An: Markus Stockhausen
> > Cc: Michael Ellerman; linuxppc-dev@lists.ozlabs.org
> > Betreff: Re: AW: How to make use of SPE instructions?
> > ...
> > With your advice I would place a enable/disable preemption call after
> > 1K of processed data. But wil that be sufficient if I only reeanble it
> > for a short timeframe like this:
> >
> >   do {
> >     disable_preemption()
> >     ... calc hashes for 1K of data with 16.000 CPU cycles (or 20us) ...
> >     enable_preemption()
> >   while (dataleft>0);
> 
> Yes, it's sufficient.  When you enable preemption it will check to see
> whether there is a pending reschedule.
> 

Hi Scott,

thanks for your helpful feedback. As you might have seen I sent a first
patch for the sha256 kernel module that takes care about preemption.

Herbert Xu noticed that my module won't run in for IPsec as all
work will be done from interrupt context. Do you have a tip how I can
mitigate the check I implemented:

static bool spe_usable(void)
{
  return !in_interrupt();
}

Intel guys have something like that

bool irq_fpu_usable(void)
{
  return !in_interrupt() ||
    interrupted_user_mode() ||
    interrupted_kernel_fpu_idle();
}

But I have no idea how to transfer it to the PPC/SPE case.

Thanks in advance.

Markus

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