From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qg0-f46.google.com (mail-qg0-f46.google.com [209.85.192.46]) by dpdk.org (Postfix) with ESMTP id 98716567F for ; Fri, 11 Sep 2015 18:04:12 +0200 (CEST) Received: by qgev79 with SMTP id v79so66055499qge.0 for ; Fri, 11 Sep 2015 09:04:12 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:date :message-id:subject:from:to:cc:content-type; bh=Etv+PY1ISUVGhzSTIW0Wq8xPYwt7Vr4eqemLUFzCwUY=; b=eF9AVGwvxMzAe2IJLi/6TvxyNxWC5de7rc+vefDoWtac4/FqMRuEhGh3Om/9tQALkc dj+y9/+9O8m1J80ufDiFqhbC30Y19dNwe09Qi8rXQphWFJcXM2GQhlkNLnQILCzAnoj9 3oRybmJfZtvE7Q9q+tZCRdA7BWf112FCXz9sskQ9gIXtAmxlsNNQ2FJwjJeFRhrFjJta DX1dtZqXWwCmtyPXXN/rboZeNiGLmNeSX9nXekQgsrx7GTUWHpXxvqEvk4EbZaDiyYBa 8A818/DYG2+FX3kZ5tj3ORRzK5Z2Bk4+Yq+LU+0Y4qvaMikPp3nHQQI1qoasWcySemwA tqoQ== X-Gm-Message-State: ALoCoQkOURzc4LuWqH+DIQMUp4pHr7iMHTQZvNWhUYDPI8nV7RyiKcF55P7Isl+43O++kkV0QbPu MIME-Version: 1.0 X-Received: by 10.140.31.135 with SMTP id f7mr63510782qgf.11.1441987451935; Fri, 11 Sep 2015 09:04:11 -0700 (PDT) Received: by 10.55.123.131 with HTTP; Fri, 11 Sep 2015 09:04:11 -0700 (PDT) Received: by 10.55.123.131 with HTTP; Fri, 11 Sep 2015 09:04:11 -0700 (PDT) In-Reply-To: <55F2F6A9.6080405@cloudius-systems.com> References: <1439489195-31553-1-git-send-email-vladz@cloudius-systems.com> <55F2E448.1070602@6wind.com> <55F2E997.5050009@cloudius-systems.com> <1762144.1LKiyImgC1@xps13> <55F2F6A9.6080405@cloudius-systems.com> Date: Fri, 11 Sep 2015 19:04:11 +0300 Message-ID: From: Vladislav Zolotarov To: Avi Kivity Content-Type: text/plain; charset=UTF-8 X-Content-Filtered-By: Mailman/MimeDel 2.1.15 Cc: dev@dpdk.org Subject: Re: [dpdk-dev] [PATCH v1] ixgbe_pmd: forbid tx_rs_thresh above 1 for all NICs but 82598 X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 11 Sep 2015 16:04:13 -0000 On Sep 11, 2015 6:43 PM, "Avi Kivity" wrote: > > On 09/11/2015 06:12 PM, Vladislav Zolotarov wrote: >> >> >> On Sep 11, 2015 5:55 PM, "Thomas Monjalon" wrote: >> > >> > 2015-09-11 17:47, Avi Kivity: >> > > On 09/11/2015 05:25 PM, didier.pallard wrote: >> > > > On 08/25/2015 08:52 PM, Vlad Zolotarov wrote: >> > > >> >> > > >> Helin, the issue has been seen on x540 devices. Pls., see a chapter >> > > >> 7.2.1.1 of x540 devices spec: >> > > >> >> > > >> A packet (or multiple packets in transmit segmentation) can span any >> > > >> number of >> > > >> buffers (and their descriptors) up to a limit of 40 minus WTHRESH >> > > >> minus 2 (see >> > > >> Section 7.2.3.3 for Tx Ring details and section Section 7.2.3.5.1 for >> > > >> WTHRESH >> > > >> details). For best performance it is recommended to minimize the >> > > >> number of buffers >> > > >> as possible. >> > > >> >> > > >> Could u, pls., clarify why do u think that the maximum number of data >> > > >> buffers is limited by 8? >> > > >> >> > > >> thanks, >> > > >> vlad >> > > > >> > > > Hi vlad, >> > > > >> > > > Documentation states that a packet (or multiple packets in transmit >> > > > segmentation) can span any number of >> > > > buffers (and their descriptors) up to a limit of 40 minus WTHRESH >> > > > minus 2. >> > > > >> > > > Shouldn't there be a test in transmit function that drops properly the >> > > > mbufs with a too large number of >> > > > segments, while incrementing a statistic; otherwise transmit function >> > > > may be locked by the faulty packet without >> > > > notification. >> > > > >> > > >> > > What we proposed is that the pmd expose to dpdk, and dpdk expose to the >> > > application, an mbuf check function. This way applications that can >> > > generate complex packets can verify that the device will be able to >> > > process them, and applications that only generate simple mbufs can avoid >> > > the overhead by not calling the function. >> > >> > More than a check, it should be exposed as a capability of the port. >> > Anyway, if the application sends too much segments, the driver must >> > drop it to avoid hang, and maintain a dedicated statistic counter to allow >> > easy debugging. >> >> I agree with Thomas - this should not be optional. Malformed packets should be dropped. In the icgbe case it's a very simple test - it's a single branch per packet so i doubt that it could impose any measurable performance degradation. >> >> > > A drop allows the application no chance to recover. The driver must either provide the ability for the application to know that it cannot accept the packet, or it must fix it up itself. An appropriate statistics counter would be a perfect tool to detect such issues. Knowingly sending a packet that will cause a HW to hang is not acceptable.