Xiao-Feng Li wrote:
2) I have to use 3 params for fast path helper because slow helper
(gc_heap_slot_write_ref) requires 3 params.
Mikhail, we need a simpler helper. The current helper is used for a
full barrier including both the fast-path and slow-path. It's
undesirable.
Excuse me if I'm missing some details here, but surely the number of
parameters to the write barrier helper is unimportant (well, within
limits) ? Since the helper (by definition) is inlined, there is no real
parameter passing going on, and unused parameters will simply be
optimized away.
And given that the fast-path, by definition is fast, then surely calling
it when you know that the slow-path will be taken is virtually zero
overhead ?
I was also under the impression that Moxie required the inlined helpers,
and since Moxie uses MMTk, won't it need the additional parameters ?
> And the API gc_heap_slot_write_ref() is called sometimes
by VM even for a non-generational GC. So its implementation is not
efficient. I'd suggest to have a simpler helper for slow-path-only:
gc_slot_remember( Managed_Object_Handle *p_slot,
Managed_Object_Handle p_target ). It is not a barrier, but only
remember the slot. For GCv5, the concrete code should look like:
>
void gc_slot_rem( Managed_Object_Handle *p_slot,
Managed_Object_Handle p_target )
{
Mutator *mutator = (Mutator *)gc_get_tls();
mutator_remset_add_entry(mutator, (Partial_Reveal_Object**)p_slot);
}
How do you think? Thanks.
This slow path needs actually only one parameter, but initially it's
ok to give two for assertion check to make sure it should be
remembered.
Thanks,
xiaofeng
On 12/6/06, Xiao-Feng Li <[EMAIL PROTECTED]> wrote:
>
> On 12/6/06, Mikhail Fursov <[EMAIL PROTECTED]> wrote:
> > Today helpers are inlined only by SD2_OPT JIT. We can add helpers
> inlining
> > to SD1_OPT too, but helpers classes are initialized only from VMStart
> class
> > - so there will be ~1k methods compiled by SD1_OPT without helpers
> inlined
> > and we will have a problem to differentiate them.
>
> Probably we can introduce some annotations to guide the compiler for
> branch scheduling (and probably for some other scenarios as well, such
> as dead object for GC). Of course that will not be prioritized until
> some evidence shows the importance.
>
> Thanks,
> xiaofeng
>
> > On 06 Dec 2006 16:52:12 +0600, Egor Pasko <[EMAIL PROTECTED]>
wrote:
> > >
> > > On the 0x237 day of Apache Harmony Mikhail Fursov wrote:
> > > > On 06 Dec 2006 13:13:51 +0600, Egor Pasko <[EMAIL PROTECTED]>
> wrote:
> > > > >
> > > > > Jitrino.OPT relies on edge profile. The most probable edges are
> > > > > fallthrough.
> > > >
> > > > The only problem here is that vmhelpers are never recompiled
> and their
> > > IR
> > > > is estimated with heuristic based profiler. So, as JIT developer,
> I'm
> > > not
> > > > sure if a branch in Java code will be layouted as fallthrough
or as
> > > jump.
> > >
> > > That's interesting! I see no serious reasons that can stop us from
> > > profiling VM helpers. Just need the right .emconf. Or am I missing
> > > something?
> > >
> > > --
> > > Egor Pasko
> > >
> > >
> >
> >
> > --
> > Mikhail Fursov
> >
> >
>
--
Mikhail Fursov
--
Robin Garner
Dept. of Computer Science
Australian National University
http://cs.anu.edu.au/people/Robin.Garner/
