I think this is working. Patches are for linux-2.6.16. Preempt_disable
seems to be unnecesary before goto_sleep_pci so I do it later. I can do:

while [ 1 ]
do
echo >scaling_setspeed 532000
sleep 1s
echo >scaling_setspeed 997000
sleep 1s
done

on one console while on other is running:

while [ 1 ]
do
hdparm -t /dev/hda
done

Output (24MB/s is max for my drive):
dev/hda:
 Timing buffered disk reads:   60 MB in  3.02 seconds =  19.90 MB/sec
 Timing buffered disk reads:   62 MB in  3.02 seconds =  20.52 MB/sec
 Timing buffered disk reads:   68 MB in  3.01 seconds =  22.56 MB/sec
 Timing buffered disk reads:   50 MB in  3.44 seconds =  14.55 MB/sec
 Timing buffered disk reads:   70 MB in  3.07 seconds =  22.80 MB/sec




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