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List:       linux-rt
Subject:    Timing, again
From:       Daniele Lugli <danlugli () tin ! it>
Date:       1997-09-03 0:35:23
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In my previous message ("A question about timing", 8 August 1997) I was
reporting a jitter of about 100 us in the rect_wave example run on a
Pentium 133 booting RTLinux from a Jaz drive.
Now I have installed RTLinux on the HD, all the rest being unchanged,
and the jitter is only 40 us - very close to what is written in the
documentation.
In both cases, of course, I stress the system with heavy disk access,
like "find / -name nonexistent.file", "ls / -alR", "startx" and so on,
otherwise the jitter is almost null.
In both cases my ISA bus is completely empty (Jaz is SCSI on PCI).
Accepting the fact that the Jaz drive is slower than the HD, I still
don't understand how this can influence so heavily the behaviour of a
real time task, as the interrupts are only disabled really by RTLinux,
not by Linux nor by disk drivers.
Best regards,
Daniele Lugli

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