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[83.59.162.106]) by smtp.gmail.com with ESMTPSA id b189sm21686008wmb.37.2020.10.12.04.48.37 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 12 Oct 2020 04:48:37 -0700 (PDT) Subject: Re: [PATCH] hw/net: move allocation to the heap due to very large stack frame From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= To: David Gibson , Elena Afanasova References: <8f07132478469b35fb50a4706691e2b56b10a67b.camel@gmail.com> <20201010060745.GK1025389@yekko.fritz.box> Message-ID: Date: Mon, 12 Oct 2020 13:48:37 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.3.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2a00:1450:4864:20::444; envelope-from=philippe.mathieu.daude@gmail.com; helo=mail-wr1-x444.google.com X-detected-operating-system: by eggs.gnu.org: No matching host in p0f cache. That's all we know. X-Spam_score_int: -14 X-Spam_score: -1.5 X-Spam_bar: - X-Spam_report: (-1.5 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_FORGED_FROMDOMAIN=0.249, FREEMAIL_FROM=0.001, HEADER_FROM_DIFFERENT_DOMAINS=0.25, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-trivial@nongnu.org, jasowang@redhat.com, qemu-ppc@nongnu.org, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 10/12/20 1:09 PM, Philippe Mathieu-Daudé wrote: > On 10/10/20 8:07 AM, David Gibson wrote: >> On Fri, Oct 09, 2020 at 07:02:56AM -0700, Elena Afanasova wrote: >>> >From 09905773a00e417d3a37c12350d9e55466fdce8a Mon Sep 17 00:00:00 2001 >>> From: Elena Afanasova >>> Date: Fri, 9 Oct 2020 06:41:36 -0700 >>> Subject: [PATCH] hw/net: move allocation to the heap due to very >>> large stack >>>   frame >> >> Patch looks fine, but some more details of the motivation would be >> nice.  I wouldn't have thought that the size of a network packet >> counted as a "very large" stack frame by userspace standards. > > Maybe academia doing research on "super jumbo frames"? > > "Super jumbo frames ... increase the path MTU of high-performance > national research and education networks from 1500 bytes to 9000 > bytes or so, a subsequent increase, possibly to 64,000 bytes" > > (https://en.wikipedia.org/wiki/Jumbo_frame#Super_jumbo_frames) The one I was actually looking for is the IPv6 jumbogram: "An optional feature of IPv6, the jumbo payload option, allows the exchange of packets with payloads of up to one byte less than 4 GiB, by making use of a 32-bit length field." (https://en.wikipedia.org/wiki/Jumbogram)