On Út 31-05-05 01:21:37, Rene Herman wrote:
> Hi Bartlomiej.
>
> My Maxtor 6Y120P0 on AMD756 (UDMA66) normally gives me 50 MB/s according
> to hdparm -t:
>
> ===
> # hdparm -t /dev/hda
>
> /dev/hda:
> Timing buffered disk reads: 152 MB in 3.01 seconds = 50.57 MB/sec
> ===
>
> However, the second I switch on my external USB2 drive (Western Digital
> Essential 160G, connected via a PCI card USB2 controller, on a private IRQ):
>
> ===
> usb 1-3: new high speed USB device using ehci_hcd and address 3
> scsi0 : SCSI emulation for USB Mass Storage devices
> usb-storage: device found at 3
> usb-storage: waiting for device to settle before scanning
> Vendor: WD Model: 1600BB External Rev: 0412
> Type: Direct-Access ANSI SCSI revision: 00
> SCSI device sda: 312581808 512-byte hdwr sectors (160042 MB)
> sda: assuming drive cache: write through
> SCSI device sda: 312581808 512-byte hdwr sectors (160042 MB)
> sda: assuming drive cache: write through
> sda: sda1 sda2
> Attached scsi disk sda at scsi0, channel 0, id 0, lun 0
> usb-storage: device scan complete
> ===
>
> the hdparm -t result drops down to 42MB/s:
>
> ===
> # hdparm -t /dev/hda
>
> /dev/hda:
> Timing buffered disk reads: 130 MB in 3.04 seconds = 42.77 MB/sec
> ===
>
> Switching the USB2 HDD off again does not work to bring back the 50 MB/s:
>
> ===
> # eject sda
> # hdparm -t /dev/hda
>
> /dev/hda:
> Timing buffered disk reads: 128 MB in 3.01 seconds = 42.57 MB/sec
>
> [ push button ]
>
> usb 1-3: USB disconnect, address 3
>
> # hdparm -t /dev/hda
>
> /dev/hda:
> Timing buffered disk reads: 130 MB in 3.04 seconds = 42.73 MB/sec
> ===
>
> After a reboot, it's 50 MB/s again. Any idea what this is?
>
> The USB HDD is not firing interrupts or anything. It just sits idle.
> Fully repeatable on 2.6.11.11 and 2.6.12-rc5.
USB controller generating extra DMA load? Try rmmoding usb to see if
it goes away.
Pavel
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