On Jun 15, 2011, at 4:19 PM, Ira Abramov wrote:
Second, here's my problem: I have here a workstation running an Athlon
3700+, and part of my job is to occasionally write out an image file
to
USB universal card reader, testing the product of my builds. The
writing
takes forever (since I haven't discovered how to get dd to write out
the
sparse image to the CF card sparsely). Also, untill I moved the card
reader to one of the backpanel ports, the write would drag my entire
environment to a halt at the same time - even the mouse pointer gets
stuck at some point, until dd would finish. switching from front to
back
panel and adding the oflag=dsync option solved the freַ¯ing of the
userspace but not the horrible writing speeds.
I have a feeling this is a major bug with the USBstorage driver or
some
related module, but as this is old hardware running on the latest
kernel
from Ubuntu, I am surprised. Anyone got a clue?
No. It has to do with how USB is implemented in hardware. Almost every
motherboard I have seen only has 2 USB ports. Motherboards with 6 USB
ports on the back, and connectors for more on the front of the case
still have only 2 USB ports, but they have a hub built into the
motherboard.
For example, on one system I have: lspci yields:
00:10.0 USB Controller: VIA Technologies, Inc. VT82xxxxx UHCI USB 1.1
Controller (rev 62)
00:10.1 USB Controller: VIA Technologies, Inc. VT82xxxxx UHCI USB 1.1
Controller (rev 62)
00:10.2 USB Controller: VIA Technologies, Inc. USB 2.0 (rev 65)
The third USB controller is a PCI card. Now if you do a lsusb:
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 006 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 005 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
But I don't have any hubs. They are on the motherboard and the PCI card.
So if you plug the keyboard and mouse into the same port as the memory
stick, you are doing two things.
The first is you are slowing the memory stick down to the speed of the
keyboard and mouse, usually 12mbits per second.
The second is that you are blocking IO to the keyboard and mouse while
the disk is busy.
Geoff.
--
Geoffrey S. Mendelson, N3OWJ/4X1GM
Making your enemy reliant on software you support is the best revenge.
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