On 2017/06/16 03:16PM, Michael Ellerman wrote:
> "Naveen N. Rao" <naveen.n....@linux.vnet.ibm.com> writes:
>
> > diff --git a/arch/powerpc/kernel/exceptions-64s.S
> > b/arch/powerpc/kernel/exceptions-64s.S
> > index ae418b85c17c..17ee701b8336 100644
> > --- a/arch/powerpc/kernel/exceptions-64s.S
> > +++ b/arch/powerpc/kernel/exceptions-64s.S
> > @@ -1442,7 +1440,9 @@ do_hash_page:
> >
> > /* Here we have a page fault that hash_page can't handle. */
> > handle_page_fault:
> > -11: ld r4,_DAR(r1)
> > + andis. r0,r4,DSISR_DABRMATCH@h
> > + bne- handle_dabr_fault
>
> This broke hash. Please test hash! :)
Gah! :double-face-palm:
I don't know how I missed this... (yes, I do)
>
> I added:
>
> @@ -1438,11 +1436,16 @@ do_hash_page:
>
> /* Error */
> blt- 13f
> +
> + /* Reload DSISR into r4 for the DABR check below */
> + ld r4,_DSISR(r1)
> #endif /* CONFIG_PPC_STD_MMU_64 */
>
> /* Here we have a page fault that hash_page can't handle. */
> handle_page_fault:
As always, thanks Michael!
I think we can optimize this a bit more to eliminate the loads in
handle_page_fault. Here's an incremental patch above your changes for
-next, this time boot-tested with radix and disable_radix.
- Naveen
-----
[PATCH] powerpc64/exceptions64s: Eliminate a few un-necessary memory loads
In do_hash_page(), we re-load DSISR from stack though it is still present
in register r4. Eliminate the memory load by preserving this register.
Furthermore, handler_page_fault() reloads DAR and DSISR from memory and
this is only required if we fall through from do_hash_page().
Otherwise, r3 and r4 already have DAR and DSISR loaded. Re-use those
and have do_hash_page() reload those registers when falling-through.
Signed-off-by: Naveen N. Rao <naveen.n....@linux.vnet.ibm.com>
---
arch/powerpc/kernel/exceptions-64s.S | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/arch/powerpc/kernel/exceptions-64s.S
b/arch/powerpc/kernel/exceptions-64s.S
index dd619faab862..b5182a1ef3d6 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -1426,8 +1426,8 @@ do_hash_page:
*
* at return r3 = 0 for success, 1 for page fault, negative for error
*/
+ mr r6,r4
mr r4,r12
- ld r6,_DSISR(r1)
bl __hash_page /* build HPTE if possible */
cmpdi r3,0 /* see if __hash_page succeeded */
@@ -1437,7 +1437,8 @@ do_hash_page:
/* Error */
blt- 13f
- /* Reload DSISR into r4 for the DABR check below */
+ /* Reload DAR/DSISR for handle_page_fault */
+ ld r3,_DAR(r1)
ld r4,_DSISR(r1)
#endif /* CONFIG_PPC_STD_MMU_64 */
@@ -1445,8 +1446,8 @@ do_hash_page:
handle_page_fault:
andis. r0,r4,DSISR_DABRMATCH@h
bne- handle_dabr_fault
- ld r4,_DAR(r1)
- ld r5,_DSISR(r1)
+ mr r5,r4
+ mr r4,r3
addi r3,r1,STACK_FRAME_OVERHEAD
bl do_page_fault
cmpdi r3,0
--
2.13.1
