how to test the performance of PIO and DMA

Josip Loncaric josip at
Mon Feb 4 08:23:43 PST 2002

> > Title: how to test the performance of PIO and DMA
>         use hdparm for simple easy tests and watch your resulting
>         transfer speed

You may also want to monitor your CPU load: there is a huge difference
in CPU overhead between PIO and DMA modes.  The standard hdparm test is
too brief to see this, but running something disk intensive and long
(e.g. "badblocks") allows you to compare CPU load.

Moreover, I think that DMA gives you CRC checking for data going over
the IDE cable while PIO does not.  DMA is a clear winner, unless you
have one of the old drives (e.g. Seagate ST36530A) known to have
hardware bugs in DMA mode.  Very old motherboard chipsets may limit DMA
performance as well.  New/recent stuff should work fine.


Dr. Josip Loncaric, Research Fellow               mailto:josip at
ICASE, Mail Stop 132C           PGP key at
NASA Langley Research Center             mailto:j.loncaric at
Hampton, VA 23681-2199, USA    Tel. +1 757 864-2192  Fax +1 757 864-6134

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