Re: Unresponiveness of 2.4.16

[Andrew Morton]

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.