| Message ID | 1537970184-44348-5-git-send-email-julien.thierry@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Ensure stack is aligned for kernel entries | expand |
On Wed, Sep 26, 2018 at 02:56:21PM +0100, Julien Thierry wrote: > Avoiding stack alignment for already aligned stack can give a small > performance boost. > > Branch out of the aligning code when the stack is known to be aligned. > > Signed-off-by: Julien Thierry <julien.thierry@arm.com> > --- > arch/arm64/kernel/entry.S | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S > index 8fb66e4..bd8d52c 100644 > --- a/arch/arm64/kernel/entry.S > +++ b/arch/arm64/kernel/entry.S > @@ -61,6 +61,10 @@ > > .macro force_stack_align > xchg_sp x0 > + > + tst x0, #0xf > + b.eq 0f > + > str x1, [x0] // store x1 far away from S_SP > > // aligned_sp[S_SP] = old_sp > @@ -69,6 +73,11 @@ > > ldr x1, [x0] > bic x0, x0, #0xf // x0 = aligned_sp > + b 1f > + > +0: > + str x0, [x0, #S_SP] > +1: I couldn't figure out a better way to do this, but please remove the empty lines that you're adding here. With that: Acked-by: Will Deacon <will.deacon@arm.com> Will
On 07/11/18 21:59, Will Deacon wrote: > On Wed, Sep 26, 2018 at 02:56:21PM +0100, Julien Thierry wrote: >> Avoiding stack alignment for already aligned stack can give a small >> performance boost. >> >> Branch out of the aligning code when the stack is known to be aligned. >> >> Signed-off-by: Julien Thierry <julien.thierry@arm.com> >> --- >> arch/arm64/kernel/entry.S | 9 +++++++++ >> 1 file changed, 9 insertions(+) >> >> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S >> index 8fb66e4..bd8d52c 100644 >> --- a/arch/arm64/kernel/entry.S >> +++ b/arch/arm64/kernel/entry.S >> @@ -61,6 +61,10 @@ >> >> .macro force_stack_align >> xchg_sp x0 >> + >> + tst x0, #0xf >> + b.eq 0f >> + >> str x1, [x0] // store x1 far away from S_SP >> >> // aligned_sp[S_SP] = old_sp >> @@ -69,6 +73,11 @@ >> >> ldr x1, [x0] >> bic x0, x0, #0xf // x0 = aligned_sp >> + b 1f >> + >> +0: >> + str x0, [x0, #S_SP] >> +1: > > I couldn't figure out a better way to do this, but please remove the empty > lines that you're adding here. With that: > Sure, I'll do that. > Acked-by: Will Deacon <will.deacon@arm.com> > Thanks,
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 8fb66e4..bd8d52c 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -61,6 +61,10 @@ .macro force_stack_align xchg_sp x0 + + tst x0, #0xf + b.eq 0f + str x1, [x0] // store x1 far away from S_SP // aligned_sp[S_SP] = old_sp @@ -69,6 +73,11 @@ ldr x1, [x0] bic x0, x0, #0xf // x0 = aligned_sp + b 1f + +0: + str x0, [x0, #S_SP] +1: xchg_sp x0 .endm
Avoiding stack alignment for already aligned stack can give a small performance boost. Branch out of the aligning code when the stack is known to be aligned. Signed-off-by: Julien Thierry <julien.thierry@arm.com> --- arch/arm64/kernel/entry.S | 9 +++++++++ 1 file changed, 9 insertions(+)