On Tue, Mar 22, 2005 at 03:57:08PM -0500, Dan Malek wrote:
>
> On Mar 22, 2005, at 8:04 AM, Marcelo Tosatti wrote:
>
> >I'm quite puzzled. Why v2.6 calls the "tlbie" instruction 100-or-so
> >less times than v2.4 ?
That was rather a _factor_ of "100-or-so" less.
> Oh my ... I'm more worried about the high number of TLB misses
> in 2.6 compared to 2.4. That's really bad.
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 ?
> How did you instrument the tlbie measurement?
By a counter at the end of _tlbie function, similar to other counters which
you suggested.
> It could be that 2.4 used lots more 'tlbia' which were replaced by tlbie in
> 2.6.
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.
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):
static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next,
struct task_struct *tsk)
{
#ifdef CONFIG_ALTIVEC
asm volatile (
BEGIN_FTR_SECTION
"dssall;\n"
#ifndef CONFIG_POWER4
"sync;\n" /* G4 needs a sync here, G5 apparently not */
#endif
END_FTR_SECTION_IFSET(CPU_FTR_ALTIVEC)
: : );
#endif /* CONFIG_ALTIVEC */
tsk->thread.pgdir = next->pgd;
/* No need to flush userspace segments if the mm doesnt change */
if (prev == next) <--------------
return; <--------------
/* Setup new userspace context */
get_mmu_context(next);
set_context(next->context, next->pgd);
}
I'm about to disable it and retry.
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.
I'll continue tracking it down - any help is appreciated.
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.
How can I reproduce it again? Guillaume, what kernel version are you using?
