drm/selftests/mm: reduce per-function stack usage

Message ID 20200529201534.474853-1-arnd@arndb.de
State New
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Series
  • drm/selftests/mm: reduce per-function stack usage
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Commit Message

Arnd Bergmann May 29, 2020, 8:15 p.m.
The check_reserve_boundaries() function has a large array on the stack,
over 500 bytes. It gets inlined into __igt_reserve, which has multiple
other large structures as well but stayed just under the stack size
warning limit of 1024 bytes until one more member got added to struct
drm_mm_node, causing a warning:

drivers/gpu/drm/selftests/test-drm_mm.c:371:12: error:
stack frame size of 1032 bytes in function '__igt_reserve' [-Werror,-Wframe-larger-than=]

As far as I can tell, this is not nice but will not be called from
a context that is already low for the kernel stack, so just annotate
the inner function as noinline_for_stack to ensure that each function
by itself stays under the warning limit.

Fixes: 0cdea4455acd ("drm/mm: optimize rb_hole_addr rbtree search")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

---
 drivers/gpu/drm/selftests/test-drm_mm.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

-- 
2.26.2

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Comments

Chris Wilson May 29, 2020, 8:26 p.m. | #1
Quoting Arnd Bergmann (2020-05-29 21:15:26)
> The check_reserve_boundaries() function has a large array on the stack,

> over 500 bytes. It gets inlined into __igt_reserve, which has multiple

> other large structures as well but stayed just under the stack size

> warning limit of 1024 bytes until one more member got added to struct

> drm_mm_node, causing a warning:

> 

> drivers/gpu/drm/selftests/test-drm_mm.c:371:12: error:

> stack frame size of 1032 bytes in function '__igt_reserve' [-Werror,-Wframe-larger-than=]

> 

> As far as I can tell, this is not nice but will not be called from

> a context that is already low for the kernel stack, so just annotate

> the inner function as noinline_for_stack to ensure that each function

> by itself stays under the warning limit.

> 

> Fixes: 0cdea4455acd ("drm/mm: optimize rb_hole_addr rbtree search")

> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

> ---

>  drivers/gpu/drm/selftests/test-drm_mm.c | 5 ++---

>  1 file changed, 2 insertions(+), 3 deletions(-)

> 

> diff --git a/drivers/gpu/drm/selftests/test-drm_mm.c b/drivers/gpu/drm/selftests/test-drm_mm.c

> index 9aabe82dcd3a..30108c330db8 100644

> --- a/drivers/gpu/drm/selftests/test-drm_mm.c

> +++ b/drivers/gpu/drm/selftests/test-drm_mm.c

> @@ -323,9 +323,8 @@ static bool expect_reserve_fail(struct drm_mm *mm, struct drm_mm_node *node)

>         return false;

>  }

>  

> -static bool check_reserve_boundaries(struct drm_mm *mm,

> -                                    unsigned int count,

> -                                    u64 size)

> +static noinline_for_stack bool

> +check_reserve_boundaries(struct drm_mm *mm, unsigned int count, u64 size)

>  {

>         const struct boundary {


It's this const [] right? Hmm, if we felt adventurous that could be a
small set of multiplication factors (0, -1, 1, count, count+1, ...) and
made static.
-Chris
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Arnd Bergmann May 29, 2020, 8:43 p.m. | #2
On Fri, May 29, 2020 at 10:26 PM Chris Wilson <chris@chris-wilson.co.uk> wrote:
> Quoting Arnd Bergmann (2020-05-29 21:15:26)


> >

> > diff --git a/drivers/gpu/drm/selftests/test-drm_mm.c b/drivers/gpu/drm/selftests/test-drm_mm.c

> > index 9aabe82dcd3a..30108c330db8 100644

> > --- a/drivers/gpu/drm/selftests/test-drm_mm.c

> > +++ b/drivers/gpu/drm/selftests/test-drm_mm.c

> > @@ -323,9 +323,8 @@ static bool expect_reserve_fail(struct drm_mm *mm, struct drm_mm_node *node)

> >         return false;

> >  }

> >

> > -static bool check_reserve_boundaries(struct drm_mm *mm,

> > -                                    unsigned int count,

> > -                                    u64 size)

> > +static noinline_for_stack bool

> > +check_reserve_boundaries(struct drm_mm *mm, unsigned int count, u64 size)

> >  {

> >         const struct boundary {

>

> It's this const [] right? Hmm, if we felt adventurous that could be a

> small set of multiplication factors (0, -1, 1, count, count+1, ...) and

> made static.


That was my first thought, but I couldn't figure out whether 'count'
could be replaced by any compile-time constant.

      Arnd
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Chris Wilson May 29, 2020, 9:36 p.m. | #3
Quoting Arnd Bergmann (2020-05-29 21:43:47)
> On Fri, May 29, 2020 at 10:26 PM Chris Wilson <chris@chris-wilson.co.uk> wrote:

> > Quoting Arnd Bergmann (2020-05-29 21:15:26)

> 

> > >

> > > diff --git a/drivers/gpu/drm/selftests/test-drm_mm.c b/drivers/gpu/drm/selftests/test-drm_mm.c

> > > index 9aabe82dcd3a..30108c330db8 100644

> > > --- a/drivers/gpu/drm/selftests/test-drm_mm.c

> > > +++ b/drivers/gpu/drm/selftests/test-drm_mm.c

> > > @@ -323,9 +323,8 @@ static bool expect_reserve_fail(struct drm_mm *mm, struct drm_mm_node *node)

> > >         return false;

> > >  }

> > >

> > > -static bool check_reserve_boundaries(struct drm_mm *mm,

> > > -                                    unsigned int count,

> > > -                                    u64 size)

> > > +static noinline_for_stack bool

> > > +check_reserve_boundaries(struct drm_mm *mm, unsigned int count, u64 size)

> > >  {

> > >         const struct boundary {

> >

> > It's this const [] right? Hmm, if we felt adventurous that could be a

> > small set of multiplication factors (0, -1, 1, count, count+1, ...) and

> > made static.

> 

> That was my first thought, but I couldn't figure out whether 'count'

> could be replaced by any compile-time constant.


I just realised I sent a sketch of a patch to the wrong place. If we
replace struct boundary with { int start; int size; const char *name; }
that should reduce it from 408 to 272. (Where start, size are the
multiples.)

Probably not worth the hassle, the saving is too small overall leaving
it uncomfortably close to a future warning.

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>

-Chris
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Patch

diff --git a/drivers/gpu/drm/selftests/test-drm_mm.c b/drivers/gpu/drm/selftests/test-drm_mm.c
index 9aabe82dcd3a..30108c330db8 100644
--- a/drivers/gpu/drm/selftests/test-drm_mm.c
+++ b/drivers/gpu/drm/selftests/test-drm_mm.c
@@ -323,9 +323,8 @@  static bool expect_reserve_fail(struct drm_mm *mm, struct drm_mm_node *node)
 	return false;
 }
 
-static bool check_reserve_boundaries(struct drm_mm *mm,
-				     unsigned int count,
-				     u64 size)
+static noinline_for_stack bool
+check_reserve_boundaries(struct drm_mm *mm, unsigned int count, u64 size)
 {
 	const struct boundary {
 		u64 start, size;