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[107.215.223.229]) by smtp.gmail.com with ESMTPSA id f12sm1663434ooh.38.2021.07.15.22.51.12 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Thu, 15 Jul 2021 22:51:13 -0700 (PDT) Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 14.0 \(3654.100.0.2.22\)) From: Bakul Shah In-Reply-To: Date: Thu, 15 Jul 2021 22:51:11 -0700 Content-Transfer-Encoding: 7bit Message-Id: References: <213a4c11-3ab2-4b4a-8d6b-b52105a19711@localhost> <5777F7E6-062B-4C5A-9C98-36FFE6AC3414@stdio.com> To: "Theodore Y. Ts'o" X-Mailer: Apple Mail (2.3654.100.0.2.22) Subject: Re: [TUHS] 386BSD released X-BeenThere: tuhs@minnie.tuhs.org X-Mailman-Version: 2.1.26 Precedence: list List-Id: The Unix Heritage Society mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: The Eunuchs Hysterical Society Errors-To: tuhs-bounces@minnie.tuhs.org Sender: "TUHS" On Jul 15, 2021, at 9:25 PM, Theodore Y. Ts'o wrote: > > I remember a friendly rivalry that I had with Bruce D. Evans in > Australia, who was working on the serial driver for FreeBSD, where we > would exchange tips and techniques for making the serial driver on our > respective OS's more CPU efficient. (The metric was to see who could > most reduce the system overhead of the serial interrupt and tty layers > when running a C-Kermit file transfer over a pair of RS-232 ports > connected via a loopback cable.) It was a lot of fun, and we both > gained a lot from the exchange of ideas, but finally, I came up with > an idea (flip buffers) that really reduced Linux's serial/tty > overhead, but which Bruce couldn't match in FreeBSD, because the > FreeBSD core team thought that clists were handed down from Mount > Olympus by the Gods of BSD, and making that kind of change in the tty > layer was tantamount to heresy. Heh. Dave Yost wrote the serial driver for our 4 port serial card @ Fortune (1981-82). Later chips like NS16550 had 16 char on chip buffers but we back then we used a Moto SIO chip that had only one char buffer. IIRC, he used two tricks. One was "partially evaluated" xmit/recv handlers so that each port got its own xmit/recv functions, with hand-crafted instructions (in hex, no less!) just right for a given port and all the interry t handler . The do was transfer a char from/to the buffer it (lready knew about. The other was he increased the cblock size from 8 to 128 (what a clist points to). He says he described this design to dmr who said why not?! With this design Yost's code was able to handle 4 full-duplex 9600 baud streams at full-speed. Not bad for a 5.6Mhz clock machine!