On Wed, 23 Mar 2005, Oliver Korpilla wrote:
What can you read out of this? (straight from dmesg)
It looks like it is using DMA. What is the output of hdparm -tT <device>? I get:
galileo:~# hdparm -tT /dev/sda
/dev/sda:
Timing cached reads: 2536 MB in 2.00 seconds = 1266.93 MB/sec
HDIO_DRIVE_CMD(null) (wait for flush complete) failed: Inappropriate ioctl for device
Timing buffered disk reads: 172 MB in 3.03 seconds = 56.74 MB/sec
HDIO_DRIVE_CMD(null) (wait for flush complete) failed: Inappropriate ioctl for device
More importantly, CPU usage jumps sharply up when hdparm is timing cached reads, with more than 80% cpu usage in system calls, which is expected since it is essentially reading as fast as it can from RAM; then it drops back to about 5% when timing buffered disk reads, which shows that DMA is indeed being used.
bye Giacomo
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