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[35.245.46.111]) by smtp.gmail.com with ESMTPSA id 71dfb90a1353d-5ea9b518bc8sm12525922e0c.11.2026.10.20.06.49.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 20 Oct 2026 06:49:15 -0700 (PDT) Date: Tue, 20 Oct 2026 09:49:15 -0400 From: Willem de Bruijn To: Kuniyuki Iwashima , 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: linux-kernel@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: 7bit Kuniyuki Iwashima wrote: > On Mon, 19 Oct 2026 23:07:58 +0000, Josh Don wrote: > > We hook udp_send_skb() and udp_v6_send_skb() using BPF fentry programs > > 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()"). > > Unlike tcp_drop_reason(), udp_send_skb() is a hot function as > inlined by FDO. > > Did you see how this change affects to udp_rr performance ? Yes, maybe I was a bit too fast in assuming that this does not meaningfully affect performance. A tcp_rr is worthwhile. Or, since these functions call ip(6)_send_skb, which cannot be inlined, perhaps a robust obviously free path is to attach BPF hooks to that (and filter on sk_type and sk_protocol).