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

From: Michael Ellerman <[email-masked]>
Date: Wed, 12 May 2010 10:36:05 +1000

On Wed, 2010-05-12 at 09:29 +1000, Michael Neuling wrote:
> 
> In message <1273561463.9209.138.camel@concordia> you wrote:
> > 
> > --=-S056dRzmrEHDBzKyyTOs
> > Content-Type: text/plain; charset="UTF-8"
> > Content-Transfer-Encoding: quoted-printable
> > 
> > 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.

Sure, you could theoretically still get a 4x speedup though by using the
bulk remove.

cheers