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Re: strange performance problem with a modem

On Mon, 2002-07-15 at 11:57, martin f krafft wrote:
> hi all,
> i am ssh'd in to an old 486DX2-66 with 32Mb which is happily running
> as my PPPOE router and firewall. the system load is fair, between 0.18
> and 0.50 depending on what i do.
> the machine has an external modem on ttyS0. when i start minicom,
> i can happily dial my way around.
> i also have a remote machine on which an mgetty is listening on
> a modem port. when i connect to that machine, minicom reports
> a connect, i see the mgetty login prompt... and that was about the
> last thing i can do with the system - the load shoots up to 10 or
> more. the `top` process i have running in another ssh session doesn't
> even update anymore.
> so i am wondering... an external modem really isn't a performance hog,
> and neither should be a getty connection via minicom, so what's going
> on???
> when i establish a pppd session to the same client the load doesn't go
> wild. what gives?

Could it be the the FIFO on the UART is too small, and thus 
breaks out in a storm of interrupt?

| Ron Johnson, Jr.        Home: ron.l.johnson@cox.net             |
| Jefferson, LA  USA      http://ronandheather.dhs.org:81         |
|                                                                 |
| "Experience should teach us to be most on our guard to protect  |
|  liberty when the government's purposes are beneficent. Men     |
|  born to freedom are naturally alert to repel invasion of their |
|  liberty by evil minded rulers. The greatest dangers to liberty |
|  lurk in insidious encroachment by men of zeal, well-meaning    |
|  but without understanding."                                    |
|   Justice Louis Brandeis, dissenting, Olmstead v US (1928)      |

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