Date: Sun, 29 Jun 1997 10:42:01 -0700 (PDT) From: Simon Shapiro <Shimon@i-Connect.Net> To: Bruce Evans <bde@zeta.org.au> Cc: hackers@FreeBSD.ORG, bmcgover@cisco.com Subject: Re: Clists limited to 1024 bytes? Message-ID: <XFMail.970629104201.Shimon@i-Connect.Net> In-Reply-To: <199706291005.UAA29898@godzilla.zeta.org.au>
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Hi Bruce Evans; On 29-Jun-97 you wrote: > >> Anyway, 19200 bps is not a heavy load unless there are a lot of active > >> ports. With 32 active 16550 ports it would be fairly heavy, but still > >> gives less than 6% of the throughput of a single 10Mb/s ethernet. > > > >I was thinking more (on a 16550) about what happens at 115,200, 230,400, > >and more. These are speeds we see already today with ISDN lines. > >The option of an external TA (such as a Motorola BitSRFR) is very > apealing, > >but behavior at these speeds needs careful consideration. > > > >How would you adjust the drivers to acomodate these speeds? > > 115200 was fast 10 years ago, but 230400 is currently not well support > (if you change the hardware clock to get it, then then the buffer sizes > are too small). How many ports do you need? Actually, about 15 years ago we used 384Kbps on terminals hooked to a Unix box (the tahoe was capable of supporting 256 of these, if i remember correctly), so even 10 years ago... :-) Yes, we use a doubled hardware clock. 2 ports is well enough. > >We experienced a lot of complex problems with SCSI transactions until we > >bumped the sio interrupt bufferto double its size. While performance > (on > >the sio ports - we use them only for PPP) did not drop visibly, the > strange > >incidence of dropping biodone() calls virtually stopped. > > This probably just made a race less common. It would be interesting to actually solve this mystery; how does a buffer overflow in the sio (under PPP) cause biodone to lose a completion. We know, with very high degree of certainty, that we do not lose interrupts, nor miss a call to scsi_done (which calls biodone, somehow). It appears that from scsi_done() up things drop in this case. Not every time. Nasty... Simon
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