On Wed, Nov 04, 1998 at 01:22:22PM +0100, Oliver Schindler wrote:
> > X. The default time slice in Linux is 200ms. If X uses its entire
> > time slice, you're screwed.
>
> You're wrong here. The default timeslice is 20 ms, but X or an IDE- IRQ
> can block the system up to 200-300 ms.
>
I get my info from /usr/src/linux/include/linux/sched.h:
#define DEF_PRIORITY (20*HZ/100) /* 200 ms time slices */
In non-error situations, the maximum time taken by an IDE IRQ is
the on-disk buffer size/transfer speed, which is on the order of
128 Kbytes/~10 megaytes per second, i.e., about 10 ms. This causes
serial buffer overruns with fast serial ports, thus interrupts
can be enabled during IDE transfers using hdparm -- problem
solved, unless you have a broken chipset/drive combination.
Keep in mind that timer interrupts (every 10 ms) seldom get missed.
X is a user space process, thus cannot disable interrupts, and
therefore cannot block the system.
>
> POSSIX Realtime is not enough here, because it simply works on the scheduler.
> But if
> you get IRQ's (Harddisk, network, mouse ..) the scheduler haven't got the
> slightest chance to schedule the process.
The issue here is not about missed interrupts. It is about the process
not being scheduled.
dave....
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