Most recent kernel where this bug did not occur: Distribution: Debian testing Hardware Environment: happens in three different computers Software Environment: Problem Description: When I read from USB disks, CPU usage goes to near 100% for iowait, as shown in top. It happens in an AMD64 desktop with USB 2.0, in a Pentium III desktop with USB 1.0, and also in a Centrino laptop with USB 2.0. It happens with an SD card USB adapter and also with a SATA disk USB adapter. I don't know if this is the expected behaviour for USB device in Linux but seems strange to me that I cannot use an USB disk to, for example, store DivX movies and play them. I have Googled this problem but cannot find any information of help. Please tell me if this is the expected behaviour or if it is a bug. In case of a bug I can try any patches or solutions you tell me. Thanks in advance. Steps to reproduce: plug in an USB disk and copy a big file to, for example, /dev/null
OK, forget about the bug. I have looked for more info about I/O wait and have found that this behaviour is normal. I suppose that cp should increase a lot iowait as it is copying as fast as it can, saturating the bus. In USB 2.0 systems, playing DivXs inside the USB does not increase iowait, while in USB 1.0 it does because the full USB bandwith is used, thus the CPU sits idle waiting for USB to end. Sorry again for filing the bug. I only wish there was more info about I/O wait :-(.