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[2a10:fc81:a806:d6a9::1]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-43f2075fc8esm77341215e9.30.2025.04.10.23.15.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 10 Apr 2025 23:15:05 -0700 (PDT) Date: Fri, 11 Apr 2025 08:15:03 +0200 From: Stefano Brivio To: David Gibson Subject: Re: tcp_splice SO_RCVLOWAT code; never invoked? Message-ID: <20250411081503.1f2bfca4@elisabeth> In-Reply-To: <20250411081323.5ac96909@elisabeth> References: <20250411081323.5ac96909@elisabeth> Organization: Red Hat X-Mailer: Claws Mail 4.2.0 (GTK 3.24.49; x86_64-pc-linux-gnu) MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: lfbSbRRbrIjrKZ7xHE0IP9LP3B_gyvIIhcjWd2eXFx0_1744352106 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Message-ID-Hash: 7LCFOK4CXMKO4BQJFCK7OTRB63VXLB3I X-Message-ID-Hash: 7LCFOK4CXMKO4BQJFCK7OTRB63VXLB3I X-MailFrom: sbrivio@redhat.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: passt-dev@passt.top X-Mailman-Version: 3.3.8 Precedence: list List-Id: Development discussion and patches for passt Archived-At: Archived-At: List-Archive: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: On Fri, 11 Apr 2025 08:13:23 +0200 Stefano Brivio wrote: > On Fri, 11 Apr 2025 14:54:50 +1000 > David Gibson wrote: > > > Hi Stefano, > > > > When debugging the splice EINTR bug I fixed the other day, I found the > > whole tcp_splice_sock_handler() pretty confusing to follow. So, I was > > working on some cleanups. But then I noticed something more > > specifically odd here. > > > > We've discussed the use of SO_RCVLOWAT previously. AIUI, you found it > > essential to achieve reasonable throughput and load for spliced > > connections. > > From my tests back then (never on what I ended up committing, it seems) > it wasn't needed in general, it helped only with bulk transfers that > never feel the pipe for some reason. With iperf3, I needed to play with fill, of course -- Stefano