Re: increased translation cache footprint in v2.6

Marcelo Tosatti
2005-06-27T00:06:49Z

On Mon, Jun 27, 2005 at 09:42:52AM +1000, Paul Mackerras wrote:
> Marcelo Tosatti writes:
>
> > We've noticed a slowdown while moving from v2.4 to v2.6 on a small PPC platform
> > (855T CPU running at 48Mhz, containing pair of separate I/D TLB caches with
> > 32 entries each), with a relatively recent kernel (v2.6.11).
> >
> > Test in question is a "dd" copying 16MB from /dev/zero to RAMDISK.
> >
> > Pinning an 8Mbyte TLB entry at KERNELBASE brought performance back to v2.4 levels.
>
> Why are we not pinning a large TLB entry at KERNELBASE in 2.6? Was
> that taken out to reduce the size of the tlb miss handler or
> something?

Paul,

There are buggy instances of tlbie() destroying the 8Mbyte TLB entry -
this is going to be fixed soon (its MPC8xx specific...)

I worry about machines who can't pin and/or smaller number of TLB entries.