On Monday 07 November 2005 22:39, Benjamin Herrenschmidt wrote: > On Mon, 2005-11-07 at 06:44 -0200, Marcelo Tosatti wrote: > > > > > The bug is that the zeroed TLB is not invalidated (the same reason > > for the "dcbst" misbehaviour), resulting in infinite TLBError faults. > > I see, so you are in the same situation as ia64 which has valid but > unmapped TLBs ? > > > Dan, I wonder why we just don't go back to v2.4 behaviour. It is not very > > clear to me that "two exception" speedup offsets the additional code > > required > > for "one exception" version. Have you actually done any measurements? > > What do you mean by "one exception" version ? You probably get 3 in fact > since after you have serviced the fault in the common code, you take > another fault to fill the PTE. > > In fact, you could even go back to one exception by pre-filling the TLB > in update_mmu_cache :) >
Yep. That should be the target. Remember the poor 8xx is not exactly a speed demon :). > > There is chance that the additional code ends up in the same cacheline, > > which would mean no huge gain by the "two exception" approach. Might be > > even harmful for performance (you need two exceptions instead of one > > after all). > > > > The "two exception" approach requires a TLB flush (to nuke the zeroed) > > at each PTE update for correct behaviour (which BTW is another slowdown): > > I think the current code, even with your fix, is sub-optimal. But of > course, the only way to be sure is to do real measurements > > Ben. > > The TLB flush is bogus IMO. I'm going to try the last patch by marcelo to see if it works for me. Pantelis.