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Mon, 2 Feb 2026 17:32:17 +0100 (CET) Message-ID: Subject: Re: [PATCH 2/2] media: rkvdec: reduce stack usage in rkvdec_init_v4l2_vp9_count_tbl() From: Nicolas Dufresne To: Arnd Bergmann , Detlev Casanova , Ezequiel Garcia , Mauro Carvalho Chehab , Heiko Stuebner , Nathan Chancellor Cc: Arnd Bergmann , Nick Desaulniers , Bill Wendling , Justin Stitt , Hans Verkuil , linux-media@vger.kernel.org, linux-rockchip@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev, Jonas Karlman , Alex Bee Date: Mon, 02 Feb 2026 11:32:16 -0500 In-Reply-To: <20260202094804.1231706-2-arnd@kernel.org> References: <20260202094804.1231706-1-arnd@kernel.org> <20260202094804.1231706-2-arnd@kernel.org> Autocrypt: addr=nicolas.dufresne@collabora.com; prefer-encrypt=mutual; keydata=mDMEaCN2ixYJKwYBBAHaRw8BAQdAM0EHepTful3JOIzcPv6ekHOenE1u0vDG1gdHFrChD /e0J05pY29sYXMgRHVmcmVzbmUgPG5pY29sYXNAbmR1ZnJlc25lLmNhPoicBBMWCgBEAhsDBQsJCA cCAiICBhUKCQgLAgQWAgMBAh4HAheABQkJZfd1FiEE7w1SgRXEw8IaBG8S2UGUUSlgcvQFAmibrjo CGQEACgkQ2UGUUSlgcvQlQwD/RjpU1SZYcKG6pnfnQ8ivgtTkGDRUJ8gP3fK7+XUjRNIA/iXfhXMN abIWxO2oCXKf3TdD7aQ4070KO6zSxIcxgNQFtDFOaWNvbGFzIER1ZnJlc25lIDxuaWNvbGFzLmR1Z nJlc25lQGNvbGxhYm9yYS5jb20+iJkEExYKAEECGwMFCwkIBwICIgIGFQoJCAsCBBYCAwECHgcCF4 AWIQTvDVKBFcTDwhoEbxLZQZRRKWBy9AUCaCyyxgUJCWX3dQAKCRDZQZRRKWBy9ARJAP96pFmLffZ smBUpkyVBfFAf+zq6BJt769R0al3kHvUKdgD9G7KAHuioxD2v6SX7idpIazjzx8b8rfzwTWyOQWHC AAS0LU5pY29sYXMgRHVmcmVzbmUgPG5pY29sYXMuZHVmcmVzbmVAZ21haWwuY29tPoiZBBMWCgBBF iEE7w1SgRXEw8IaBG8S2UGUUSlgcvQFAmibrGYCGwMFCQll93UFCwkIBwICIgIGFQoJCAsCBBYCAw ECHgcCF4AACgkQ2UGUUSlgcvRObgD/YnQjfi4+L8f4fI7p1pPMTwRTcaRdy6aqkKEmKsCArzQBAK8 bRLv9QjuqsE6oQZra/RB4widZPvphs78H0P6NmpIJ Organization: Collabora Canada Content-Type: multipart/signed; micalg="pgp-sha512"; protocol="application/pgp-signature"; boundary="=-2jK0PyPR5gtYSVPZSaBh" User-Agent: Evolution 3.58.2 (3.58.2-1.fc43) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 --=-2jK0PyPR5gtYSVPZSaBh Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Le lundi 02 f=C3=A9vrier 2026 =C3=A0 10:47 +0100, Arnd Bergmann a =C3=A9cri= t=C2=A0: > From: Arnd Bergmann >=20 > The deeply nested loop in rkvdec_init_v4l2_vp9_count_tbl() needs a lot > of registers, so when the clang register allocator runs out, it ends up > spilling countless temporaries to the stack: >=20 > drivers/media/platform/rockchip/rkvdec/rkvdec-vp9.c:966:12: error: stack = frame size (1472) exceeds limit (1280) in 'rkvdec_vp9_start' [-Werror,-Wfra= me-larger-than] >=20 > Marking this function as noinline_for_stack keeps it out of > rkvdec_vp9_start(), giving the compiler more room for optimization. >=20 > The resulting code is good enough that both the total stack usage > and the loop get enough better to stay under the warning limit, > though it's still slow, and would need a larger rework if this > function ends up being called in a fast path. >=20 > Signed-off-by: Arnd Bergmann Reviewed-by: Nicolas Dufresne > --- > =C2=A0drivers/media/platform/rockchip/rkvdec/rkvdec-vp9.c | 3 ++- > =C2=A01 file changed, 2 insertions(+), 1 deletion(-) >=20 > diff --git a/drivers/media/platform/rockchip/rkvdec/rkvdec-vp9.c b/driver= s/media/platform/rockchip/rkvdec/rkvdec-vp9.c > index ba51a7c2fe55..1c875d5a2bac 100644 > --- a/drivers/media/platform/rockchip/rkvdec/rkvdec-vp9.c > +++ b/drivers/media/platform/rockchip/rkvdec/rkvdec-vp9.c > @@ -893,7 +893,8 @@ static void rkvdec_vp9_done(struct rkvdec_ctx *ctx, > =C2=A0 update_ctx_last_info(vp9_ctx); > =C2=A0} > =C2=A0 > -static void rkvdec_init_v4l2_vp9_count_tbl(struct rkvdec_ctx *ctx) > +static noinline_for_stack void > +rkvdec_init_v4l2_vp9_count_tbl(struct rkvdec_ctx *ctx) > =C2=A0{ > =C2=A0 struct rkvdec_vp9_ctx *vp9_ctx =3D ctx->priv; > =C2=A0 struct rkvdec_vp9_intra_frame_symbol_counts *intra_cnts =3D vp9_ct= x->count_tbl.cpu; --=-2jK0PyPR5gtYSVPZSaBh Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- iHUEABYKAB0WIQTvDVKBFcTDwhoEbxLZQZRRKWBy9AUCaYDRkAAKCRDZQZRRKWBy 9HFyAP0RF5b0OenNAGH35mTowVmYp7pBvzgVyYN7ehX7jmx8VAEAw6AY+q+q1f2m VfoYBMjnRCRr5g/hOebJT5oXUy814QA= =fZxd -----END PGP SIGNATURE----- --=-2jK0PyPR5gtYSVPZSaBh--