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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Willem de Bruijn , "Bezdeka, Florian" , Donald Hunter , Jonathan Corbet , Bjorn Topel , "Karlsson, Magnus" , "Fijalkowski, Maciej" , Jonathan Lemon , Andrew Lunn , Alexei Starovoitov , Daniel Borkmann , Jesper Dangaard Brouer , John Fastabend , "Damato, Joe" , Stanislav Fomichev , Xuan Zhuo , Mina Almasry , Daniel Jurgens , Andrii Nakryiko , Eduard Zingerman , Mykola Lysenko , Martin KaFai Lau , Song Liu , Yonghong Song , KP Singh , Hao Luo , Jiri Olsa , Shuah Khan , Alexandre Torgue , Jose Abreu , Maxime Coquelin , "Nguyen, Anthony L" , "Kitszel, Przemyslaw" , Faizal Rahim , Choong Yong Liang Thread-Topic: [PATCH bpf-next v12 5/5] igc: Add launch time support to XDP ZC Thread-Index: AQHbgFYjDDsvmh2P3kix+y3ANQFC5rNnwgkggAAVioCABE328A== Date: Mon, 10 Mar 2025 08:08:27 +0000 Message-ID: References: <20250216093430.957880-1-yoong.siang.song@intel.com> <20250216093430.957880-6-yoong.siang.song@intel.com> In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: msip_labels: MSIP_Label_9d258917-277f-42cd-a3cd-14c4e9ee58bc_ActionId=32c776a1-e37e-408e-8746-b3b86ed4e75a;MSIP_Label_9d258917-277f-42cd-a3cd-14c4e9ee58bc_ContentBits=0;MSIP_Label_9d258917-277f-42cd-a3cd-14c4e9ee58bc_Enabled=true;MSIP_Label_9d258917-277f-42cd-a3cd-14c4e9ee58bc_Method=Standard;MSIP_Label_9d258917-277f-42cd-a3cd-14c4e9ee58bc_Name=restricted;MSIP_Label_9d258917-277f-42cd-a3cd-14c4e9ee58bc_SetDate=2025-03-07T13:03:43Z;MSIP_Label_9d258917-277f-42cd-a3cd-14c4e9ee58bc_SiteId=38ae3bcd-9579-4fd4-adda-b42e1495d55a;MSIP_Label_9d258917-277f-42cd-a3cd-14c4e9ee58bc_Tag=10, 3, 0, 1; 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emergency; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-doc@vger.kernel.org" , "bpf@vger.kernel.org" , "linux-kselftest@vger.kernel.org" , "linux-stm32@st-md-mailman.stormreply.com" , "linux-arm-kernel@lists.infradead.org" , "intel-wired-lan@lists.osuosl.org" , "xdp-hints@xdp-project.net" X-Mailman-Version: 3.3.10 Precedence: list Subject: [xdp-hints] Re: [PATCH bpf-next v12 5/5] igc: Add launch time support to XDP ZC List-Id: XDP hardware hints design discussion Archived-At: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: > -----Original Message----- > From: Song, Yoong Siang > Sent: Friday, March 7, 2025 3:21 PM >=20 > On Friday, March 7, 2025 9:25 PM, Bouska, Zdenek > wrote: >=20 > [...] >=20 > >> @@ -2996,7 +3035,13 @@ static void igc_xdp_xmit_zc(struct igc_ring *ri= ng) > >> ntu =3D ring->next_to_use; > >> budget =3D igc_desc_unused(ring); > >> > >> - while (xsk_tx_peek_desc(pool, &xdp_desc) && budget--) { > >> + /* Packets with launch time require one data descriptor and one cont= ext > >> + * descriptor. When the launch time falls into the next Qbv cycle, w= e > >> + * may need to insert an empty packet, which requires two more > >> + * descriptors. Therefore, to be safe, we always ensure we have at l= east > >> + * 4 descriptors available. > >> + */ > >> + while (xsk_tx_peek_desc(pool, &xdp_desc) && budget >=3D 4) { > > > >I think that here is a bug: some frames could be missed if budget < 4. > >I was able to reproduce it by sending 100000x 60 B frames with minimal I= PG > >(672 ns between starts of frames) on 1Gbit/s. Always 1026 frames were no= t sent > >and were missing a AF_XDP competition. Interesting was that then even wh= en I > >sent more > >frames for hours it still was 1026 frames not sent and missing competiti= on. > > > >Bug seems to be fixed when I change this line to: > > > > while (budget >=3D 4 && xsk_tx_peek_desc(pool, &xdp_desc)) { > > > >Do you think this is a good fix? > > > >I think this bug is also in original code base, but I was only able to r= eproduce > >it with launch time. > > >=20 > Thank you for pointing out this issue and for providing a detailed > explanation of your findings. I personally agree with your proposed fix > that make sure there is enough budget in the driver, before go peek the x= sk > descriptor. Do you plan to submit bug fix patch to iwl-net? >=20 Yes, I plan to submit bug fix patch. Best regards, Zdenek Bouska -- Siemens, s.r.o Foundational Technologies