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SubjectRe: Unresponiveness of 2.4.16
Ahmed Masud wrote:
>
> Just to add to the above something I've experienced:
>
> 2.4.12 - 2.4.14 on a number of AMD Athelon 900 with 256 MB
> RAM doing serial I/O would miss data while any DISK writes would
> occure.

Two possibilities suggest themselves:

- Interrupt latency. Last time I checked (a year ago), the worst-case
interrupt latency of the IDE drivers was 80 microseconds on a 500MHz PII.
That was with `hdparm -u 1'. That's pretty good.

Could you please confirm that you're using `hdparm -u 1' against the
relevant disk?

- The serial port is working OK, but the application which is handling
serial IO is blocked on a disk read (something got paged out), and
that disk read fails to complete by the time the serial port buffer
fills up.

I'll send you a patch which makes the VM less inclined to page things
out in the presence of heavy writes, and which decreases read
latencies.

Thanks.
-
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