Date: Wed, 4 Jun 1997 01:41:35 -0700 From: John-Mark Gurney <jmg@hydrogen.nike.efn.org> To: Richard Straka <straka@inficad.com> Cc: current@FreeBSD.ORG Subject: Re: sio driver performance Message-ID: <19970604014135.27671@hydrogen.nike.efn.org> In-Reply-To: <Pine.BSI.3.95.970604001520.15234B-100000@user2.inficad.com>; from Richard Straka on Wed, Jun 04, 1997 at 12:31:54AM -0700 References: <Pine.BSI.3.95.970604001520.15234B-100000@user2.inficad.com>
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Richard Straka scribbled this message on Jun 4: > I have 2 16550A UARTS in a 486DX-33. During probing, the sio > driver properly identifies both ports as 16550A's. > > When sending sustained 115200 baud data from this machine, systat > (with vmstat option) indicates an interrupt rate of about 720/sec > with about 2% of the processor servicing interrupts. > > When receiving sustained 115200 baud data, an interrupt rate of > over 26,000/sec is indicated with about 15% of the processor going > to service interrupts. > > It appears as though the fifo is not working for the receive. In an > attempt to exhonerate the hardware, I swapped in another 16550 card > I had laying around and got the similar results. it actually is working quite nicely... if it wasn't you would see 115,200 * 2 interrupts/sec if the fifo isn't working... but what you are probably seeing is that the recieve fifo is set to 8bytes instead of 14bytes (115200*2/26000 ~= 8.8615...)... also, it's a know fact that the 16550's are kinda heavy on overhead (not as bad as a parallel port though)... if you want to do many ports at full speed you really should invest in a smarter card, like a Digiboard/Cyclom/Riscom/Stallion smart board that has larger buffers and usually supports mapped memory access... > Any help on this issue would be greatly appreciated. if you get any kernel messages about sio, then you need to start worring... if you do plan to enable multiport usage (when you get a Boca or AST compatible board) when you need to look out, and I'm about to test/improve the sio so multiport doesn't hurt as much... -- John-Mark Gurney Modem/FAX: +1 541 683 6954 Cu Networking Live in Peace, destroy Micro$oft, support free software, run FreeBSD
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