On Mon, Oct 10, 2016 at 03:21:31PM -0600, Jeff Law wrote: > On 09/30/2016 04:34 AM, Segher Boessenkool wrote: > >[ whoops, message too big, resending with the attachment compressed ] > > > >On Tue, Sep 27, 2016 at 03:14:51PM -0600, Jeff Law wrote: > >>With transposition issue addressed, the only blocker I see are some > >>simple testcases we can add to the suite. They don't have to be real > >>extensive. And one motivating example for the list archives, ideally > >>the glibc malloc case. > > > >And here is the malloc testcase. > > > >A very important (for performance) function is _int_malloc, which starts > >with > [ ... ] > THanks. What I think is important to note with this example is the bits > that were pushed into the path with the sysmalloc/alloc_perturb calls. > That's an unlikely path.
alloc_perturb is a no-op, and inlined as such: as nothing :-)
> We have to extrapolate a bit from the assembly provided. In the not
> separately shrink-wrapped version, we have a full prologue of stores and
> two instances of a full epilogue (though only one ever executes) provided.
>
> With separate shrink wrapping the (presumably) very cold path where we
> error has virtually no prologue/epilogue. That's probably a nop from a
> performance standpoint.
>
> More interesting is the path where we call sysmalloc/alloc_perturb, it's
> a cold path, but not as cold as the error path. We save/restore 4 regs
> in that case. Rather than a full prologue/epilogue. So there's clearly
> a savings there, though again, via the expect it's a cold path.
>
> Where we have to extrapolate is the hot path. Presumably on the hot
> path we're saving/restoring ~4 fewer registers. I haven't verified
> that, but that is kindof the whole point here.
We save/restore just four registers total on the hot path. And yes,
that is the point :-)
The hot exit is
.L683:
ld 14,144(1)
ld 15,152(1)
ld 25,232(1)
ld 30,272(1)
addi 3,4,16
.L673:
addi 1,1,288
blr
so four GPR restores and no LR restore. Without separate shrink-wrapping
this was
.L641:
addi 3,21,16
b .L631
[ ... ]
.L631:
addi 1,1,288
ld 29,16(1)
ld 14,-144(1)
ld 15,-136(1)
ld 16,-128(1)
ld 17,-120(1)
ld 18,-112(1)
ld 19,-104(1)
ld 20,-96(1)
ld 21,-88(1)
ld 22,-80(1)
ld 23,-72(1)
ld 24,-64(1)
mtlr 29
ld 25,-56(1)
ld 26,-48(1)
ld 27,-40(1)
ld 28,-32(1)
ld 29,-24(1)
ld 30,-16(1)
ld 31,-8(1)
blr
(18 GPRs as well as LR).
I didn't show this path because there is a whole bunch of branches with
inline asm in the way.
The sysmalloc path was
.L635:
li 4,0
.L761:
addi 1,1,288
mr 3,14
ld 14,16(1)
ld 15,-136(1)
ld 16,-128(1)
ld 17,-120(1)
ld 18,-112(1)
ld 19,-104(1)
ld 20,-96(1)
ld 21,-88(1)
ld 22,-80(1)
ld 23,-72(1)
ld 24,-64(1)
ld 25,-56(1)
mtlr 14
ld 26,-48(1)
ld 14,-144(1)
ld 27,-40(1)
ld 28,-32(1)
ld 29,-24(1)
ld 30,-16(1)
ld 31,-8(1)
b sysmalloc
and now is
.L677:
mr 3,14
ld 15,152(1)
ld 14,144(1)
ld 25,232(1)
ld 30,272(1)
li 4,0
addi 1,1,288
b sysmalloc
I attach malloc.s.{no,yes}, I hope you can stomach that. Well you
can read HP-PA, heh.
Segher
malloc.s.no.gz
Description: GNU Zip compressed data
malloc.s.yes.gz
Description: GNU Zip compressed data
