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[35.245.46.111]) by smtp.gmail.com with ESMTPSA id 71dfb90a1353d-5eac20d6aa6sm7205788e0c.7.2026.10.20.06.50.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 20 Oct 2026 06:50:32 -0700 (PDT) Date: Tue, 20 Oct 2026 09:50:32 -0400 From: Willem de Bruijn To: Jason Xing , Josh Don Cc: Willem de Bruijn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , netdev@vger.kernel.org, linux-kernel@vger.kernel.org Message-ID: In-Reply-To: References: <20261019230758.2960779-1-joshdon@google.com> Subject: Re: [PATCH] udp: Add noinline_for_tracing annotation for udp{,_v6}_send_skb() X-Mailing-List: netdev@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Jason Xing wrote: > On Tue, Oct 20, 2026 at 7:08=E2=80=AFAM Josh Don w= rote: > > > > We hook udp_send_skb() and udp_v6_send_skb() using BPF fentry program= s > > to monitor UDP transmits. Both functions are static and have two > > callers: udp{,v6}_sendmsg() and udp{,_v6}_push_pending_frames(). > > > > After an FDO profile update, udp_v6_send_skb() is now inlined into > > udpv6_sendmsg(), while an out-of-line copy remains for > > udp_v6_push_pending_frames(). The fentry program still attaches > > successfully, but it is silently bypassed for all uncorked sends. > > > > To address this, make both functions noinline explicitly for tracing,= > > as was done for tcp_drop_reason() in commit dbd5e2e79ed8 ("net: tcp: > > Add noinline_for_tracing annotation for tcp_drop_reason()"). > > > > Assisted-by: LLM > > Signed-off-by: Josh Don > = > I actually mentioned this thing a few times before. The original > thread was from Breno who tried to apply a similar change for tcp > sendmsg. The fact is until now we don't guarantee those functions > should be kept noinline like how uAPI works just for BPF prog. What I > suggested was to select a series of functions in one Doc so that we > could tell people those functions should be noinline or whatever else > just for tracing in a soft way? > = > Otherwise people would argue there are more functions that should be > done in the same way because they internally trace it. > = > Willem, Kuniyuki, any thoughts? We'll have to review hooks on a case-by-case basis for performance impact. If possible, it's preferable to select hooks that cannot be inlined. Over limiting what the compiler is allowed to do.=