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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48fe57943b2sm116227845e9.8.2026.05.16.01.48.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 16 May 2026 01:48:59 -0700 (PDT) Date: Sat, 16 May 2026 09:48:57 +0100 From: David Laight To: "Arnd Bergmann" Cc: "Alexei Starovoitov" , "Arnd Bergmann" , "Alexei Starovoitov" , "Daniel Borkmann" , "Andrii Nakryiko" , "Eduard Zingerman" , "Kumar Kartikeya Dwivedi" , "David S . Miller" , "Eric Dumazet" , "Jakub Kicinski" , "Paolo Abeni" , "Jesper Dangaard Brouer" , "John Fastabend" , "Martin KaFai Lau" , Toke =?UTF-8?B?SMO4aWxhbmQtSsO4cmdlbnNlbg==?= , "Martin KaFai Lau" , "Song Liu" , "Yonghong Song" , "Jiri Olsa" , "Simon Horman" , "Stanislav Fomichev" , bpf , Netdev , LKML Subject: Re: [PATCH] bpf: test_run: reduce kernel stack usage Message-ID: <20260516094857.2ad1c850@pumpkin> In-Reply-To: <20260515193804.4d85283b@pumpkin> References: <20260515113102.2389020-1-arnd@kernel.org> <20260515193804.4d85283b@pumpkin> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On Fri, 15 May 2026 19:38:04 +0100 David Laight wrote: > On Fri, 15 May 2026 17:15:46 +0200 > "Arnd Bergmann" wrote: >=20 > > On Fri, May 15, 2026, at 16:47, Alexei Starovoitov wrote: =20 > > > On Fri, May 15, 2026 at 4:31=E2=80=AFAM Arnd Bergmann wrote: > > > > > > 1k? > > > pahole -C xdp_test_data > > > /* size: 192, cachelines: 3, members: 9 */ > > > /* sum members: 120, holes: 1, sum holes: 56 */ > > > /* padding: 16 */ > > > /* paddings: 1, sum paddings: 36 */ > > > > > > what s390 doing to make it huge? =20 > >=20 > > I think it's a combination of cacheline alignment (256 byte > > lines) that leads to padding before 'rxq' and at the end of > > xdp_test_data, as well as CONFIG_KASAN_STACK that increases > > the stack usage further. =20 >=20 > There will also be a 'double stack frame' in order to put an > aligned item on stack. > That could be slightly larger than a stack frame and probably doesn't ^ cache line > show up in the figures. >=20 > -- David >=20