On Tue, Mar 22, 2005 at 05:53:40PM -0500, Dan Malek wrote: > > On Mar 22, 2005, at 12:58 PM, Marcelo Tosatti wrote: > > >Newbie question: What prevents the initial kernel map (tuple of 8Mbyte > >I/D-TLB entries) > >and the IMMR 8Mbyte D-TLB entry from getting unmapped by translation > >pressure, > >in case CONFIG_PIN_TLB is disabled ? > > Nothing. In fact, they are likely invalidated shortly after the kernel > page tables are set up. This was only done to ensure we could get the > kernel initialized without taking page faults.
OK. > >By a counter at the end of _tlbie function, similar to other counters > >which > >you suggested. > > OK. > > >Dont think thats the case given that v2.4 calls tlbia through > >flush_tlb_mm() at exit_mmap() > >only. And at vmalloc_free which shouldnt be called at all. > > Hmmm ... Then, the 2.6 looks to be much less efficient with the MMU > resources than 2.4 was. This is going to affect everyone, it's just > easier > to measure on this processor. Many codepaths are longer (eg. but the difference > > >I just noticed this conditional at switch_mm() (v2.6), which _can_ > >partly > >explain the reduced tlbie's (its just a guess for now, though): > > What is your guess? I don't know how this would reduce the number > of tlbie instructions, since stealing a context (as part of > get_context()) > will simply whack the whole TLB with a tlbia. On 8xx, both instructions > could be simply implemented as macros. You misunderstood: get_mmu_context() _wont_ be called if the mm structures are the same. v2.4 didnt had this optimization. > >Spent part of the day reading the MMU section of 860 manual, I think I > >have kind > >of a clue how things are supposed to work at the lowlevel now. > > :-) > > >PS: I can't reproduce the invalid TLB crash anymore. i.e. even by > >removing > >the _tlbie() at update_mmu_cache() everything is working as expected. > > Well, that's interesting. It's likely to only happen on an 860 variant > that > has the large TLB. For what reasoning? > >How can I reproduce it again? Guillaume, what kernel version are you > >using? > > It used to happen on early 2.6 versions as soon as you entered user > space programs. Will let you know of any findings...
