[Bug 575722] Re: Slow disk read performance

[danb1974]

This problem goes away when plugged in - to be more specific it has to
do with sata link power management. Now I understand I will have lower
speed while on min_power, but is it normal to have such a big difference
with and without O_DIRECT?

echo max_performance >
/sys/class/scsi_host/host0/link_power_management_policy

 Timing O_DIRECT disk reads:  594 MB in  3.00 seconds = 197.71 MB/sec
 Timing buffered disk reads:  558 MB in  3.01 seconds = 185.53 MB/sec

echo min_power > /sys/class/scsi_host/host0/link_power_management_policy

 Timing O_DIRECT disk reads:  410 MB in  3.01 seconds = 136.13 MB/sec
 Timing buffered disk reads:  212 MB in  3.01 seconds =  70.33 MB/sec

-- 
Slow disk read performance
https://bugs.launchpad.net/bugs/575722
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