From: David Laight <david.laight.linux@gmail.com>
To: "Arnd Bergmann" <arnd@arndb.de>
Cc: "Alexei Starovoitov" <alexei.starovoitov@gmail.com>,
"Arnd Bergmann" <arnd@kernel.org>,
"Alexei Starovoitov" <ast@kernel.org>,
"Daniel Borkmann" <daniel@iogearbox.net>,
"Andrii Nakryiko" <andrii@kernel.org>,
"Eduard Zingerman" <eddyz87@gmail.com>,
"Kumar Kartikeya Dwivedi" <memxor@gmail.com>,
"David S . Miller" <davem@davemloft.net>,
"Eric Dumazet" <edumazet@google.com>,
"Jakub Kicinski" <kuba@kernel.org>,
"Paolo Abeni" <pabeni@redhat.com>,
"Jesper Dangaard Brouer" <hawk@kernel.org>,
"John Fastabend" <john.fastabend@gmail.com>,
"Martin KaFai Lau" <kafai@fb.com>,
"Toke Høiland-Jørgensen" <toke@redhat.com>,
"Martin KaFai Lau" <martin.lau@linux.dev>,
"Song Liu" <song@kernel.org>,
"Yonghong Song" <yonghong.song@linux.dev>,
"Jiri Olsa" <jolsa@kernel.org>, "Simon Horman" <horms@kernel.org>,
"Stanislav Fomichev" <sdf@fomichev.me>, bpf <bpf@vger.kernel.org>,
Netdev <netdev@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] bpf: test_run: reduce kernel stack usage
Date: Fri, 15 May 2026 19:38:04 +0100 [thread overview]
Message-ID: <20260515193804.4d85283b@pumpkin> (raw)
In-Reply-To: <b387dd31-0ee5-41b9-b07a-13b718080e89@app.fastmail.com>
On Fri, 15 May 2026 17:15:46 +0200
"Arnd Bergmann" <arnd@arndb.de> wrote:
> On Fri, May 15, 2026, at 16:47, Alexei Starovoitov wrote:
> > On Fri, May 15, 2026 at 4:31 AM Arnd Bergmann <arnd@kernel.org> 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?
>
> 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.
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
show up in the figures.
-- David
next prev parent reply other threads:[~2026-05-15 18:38 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-15 11:25 [PATCH] bpf: test_run: reduce kernel stack usage Arnd Bergmann
2026-05-15 14:47 ` Alexei Starovoitov
2026-05-15 15:15 ` Arnd Bergmann
2026-05-15 16:13 ` Alexei Starovoitov
2026-05-15 18:38 ` David Laight [this message]
2026-05-16 8:48 ` David Laight
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