Messages in this thread | | | Date | Mon, 10 Mar 2003 15:35:50 +1000 | From | Douglas Gilbert <> | Subject | Re: 2.4: high system load with SG_IO on IDE-SCSI: PIO? |
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Matthias Andree wrote: > I have seen readcd ("sg driver 3.2.0") use 96% system time > for a readcd -c2scan on IDE-SCSI (ATAPI CD-ROM, Plextor > PX-4824TA 1.04, UDMA/33), Linux 2.4.19+SuSE patches > (k_athlon-2.4.19-167). > > ... > ioctl(3, 0x2285, 0xbfffec20) = 0 > ... > > The same application on a real SCSI-device with SCSI host > adaptor (aic7xxx FWIW) is way below 5% system CPU time. > > Might SG_IO use PIO on ATAPI CD-ROMs? If so, are there > patches to enable DMA? Is this at all possible with SG_IO?
> I find 96% system load is way too high for modern hardware. > (Duron/700 that is, VIA 82C686a).
SG_IO is an ioctl in the sg driver that issues scsi commands and waits for a response. The route from sg is through the scsi mid level and via ide-scsi to the ide subsystem. Nothing in the SG_IO ioctl interface addresses ATA DMA and PIO settings. They can be changed via the hdparm ** command.
The experience from the early 2.4 series was that the ide subsystem was too aggressive in its DMA settings for CD/DVD burners. [My experience with scsi devices is that disks have much better target implementations (i.e. more robust) than CD/DVD devices and scanners.] Later versions of the 2.4 series are a lot more conservative in their speed treatment of ATAPI devices. The robustness comes at the expense of system load.
** Even though a CD writer appears as /dev/scd0 with ide-scsi appropriately configured, the hdparm command can still be used on /dev/hdd (for example, if the writer is the slave on the second IDE bus).
Doug Gilbert
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