Date: Fri, 21 May 1999 12:20:54 -0700 From: Mike Smith <mike@smith.net.au> To: Zhihui Zhang <zzhang@cs.binghamton.edu> Cc: freebsd-hackers@freebsd.org Subject: Re: mmap of a network buffer Message-ID: <199905211920.MAA01832@dingo.cdrom.com> In-Reply-To: Your message of "Fri, 21 May 1999 14:15:20 EDT." <Pine.GSO.3.96.990521140950.12938A-100000@sol.cs.binghamton.edu>
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> > I really do not know how to describe the problem. But a friend here asks > me how to mmap a network buffer so that there is no need to copy the data > from user space to kernel space. We are not sure whether FreeBSD can > create a device file (mknod) for a network card, and if so, we can use the > mmap() call to do so because mmap() requires a file descriptor. We assume > that the file descriptor can be acquired by opening the network device. > If this is infeasible, is there another way to accomplish the same goal? Use sendfile() for zero-copy file transmission; in all other cases it's necessary to copy data into the kernel. Memory-mapping a network buffer makes no sense if you just think about it for a moment... There's also very little need for this under "real" circumstances; some simple tests have demonstrated we can sustain about 800Mbps throughput (UDP), and the bottleneck here seems to be checksum calculations, not copyin/out. -- \\ The mind's the standard \\ Mike Smith \\ of the man. \\ msmith@freebsd.org \\ -- Joseph Merrick \\ msmith@cdrom.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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