在Linux下打開DMA

hdparm指令,需要以Root身份執行

# hdparm /dev/hda (基本上FC3都己經預設DMA開啟)

/dev/hda:
multcount = 16 (on)
IO_support = 0 (default 16-bit)
unmaskirq = 0 (off)
using_dma = 1 (on)
keepsettings = 0 (off)
readonly = 0 (off)
readahead = 256 (on)
geometry = 15509/16/63, sectors = 8004132864, start = 0

# hdparm -d0 /dev/hda (參數d0為關閉,d1為開啟)

/dev/hda:
setting using_dma to 0 (off)
using_dma = 0 (off)

# hdparm -tT /dev/hda (DMA使用前測速)

/dev/hda:
Timing cached reads: 1196 MB in 2.00 seconds = 597.49 MB/sec
Timing buffered disk reads: 10 MB in 3.51 seconds = 2.85 MB/sec

# hdparm -tT /dev/hda (DMA使用後測速)

/dev/hda:
Timing cached reads: 1188 MB in 2.00 seconds = 593.50 MB/sec
Timing buffered disk reads: 70 MB in 3.07 seconds = 22.80 MB/sec

我們可以看到IO_support預設是關閉的,可以用-c3開啟32位元IO_support

# hdparm -c3 /dev/hda

/dev/hda:
setting 32-bit IO_support flag to 3
IO_support = 3 (32-bit w/sync)

以上指令重新開機之後就會失效,可以將指令寫到 /etc/rc.d/rc.local