Subject: Re: [PATCH 2/2] powerpc,kexec: Speedup kexec hpte tear down

From: Michael Neuling <[email-masked]>
Date: Wed, 12 May 2010 09:29:54 +1000

In message <1273561463.9209.138.camel@concordia> you wrote:
> 
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> On Tue, 2010-05-11 at 16:28 +1000, Michael Neuling wrote:
> > Currently for kexec the PTE tear down on 1TB segment systems normally
> > requires 3 hcalls for each PTE removal. On a machine with 32GB of
> > memory it can take around a minute to remove all the PTEs.
> >=20
> ..
> > -	/* TODO: Use bulk call */
> 
> ...
> > +	/* Read in batches of 4,
> > +	 * invalidate only valid entries not in the VRMA
> > +	 * hpte_count will be a multiple of 4
> > +         */
> > +	for (i =3D 0; i < hpte_count; i +=3D 4) {
> > +		lpar_rc =3D plpar_pte_read_4_raw(0, i, (void *)ptes);
> > +		if (lpar_rc !=3D H_SUCCESS)
> > +			continue;
> > +		for (j =3D 0; j < 4; j++){
> > +			if ((ptes[j].pteh & HPTE_V_VRMA_MASK) =3D=3D
> > +				HPTE_V_VRMA_MASK)
> > +				continue;
> > +			if (ptes[j].pteh & HPTE_V_VALID)
> > +				plpar_pte_remove_raw(0, i + j, 0,
> > +					&(ptes[j].pteh), &(ptes[j].ptel));
> >  		}
> 
> Have you tried using the bulk remove call, if none of the HPTEs are for
> the VRMA? Rumour was it was slower/the-same, but that may have been
> apocryphal.

No, I didn't try it.

I think the real solution is to ask FW for a new call to do it all for
us.

Mikey