low-latency patch for 2.4.15-pre5

[Andrew Morton]

A low-latency scheduling patch for 2.4.15-pre4/pre5 is at

	http://www.zip.com.au/~akpm/linux/schedlat.html#downloads

This is a general retune, retest and review.  A couple of bugs which
have crept into the patch were fixed.  ext3 support is added. Certain
code paths which were introduced into the kernel in the 2.4.9-2.4.11
timeframe have been addressed.

On a single 850MHz PIII with 768 megs of RAM and 1G of swap the worst case interrupt-to-activation scheduling latency is around 400 microseconds.
Latencies on SMP are up to 1000 microseconds.

These measurements are across extreme workloads - peak latency across an SMP
kernel build is 260 microseconds.

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