Comment 33 for bug 19711
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#33 |
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bbfa235
(Get the code!)
This may have nothing to do with bus mastering activity at all. The Linux PowerTop utility blames the radeon module for causing a lot of interrupts (60 per second) on my laptop. This appears to prevent the system from entering C3 mode. Presumably this is due to vertical blanking interrupts.
Apparently the Intel graphics driver was recently fixed to enable Vblank interrupts only when somebody was interested and not all of the time. Likely the radeon module has the same problem (actually I've noticed on another machine that mga does this as well, generates 85 interrupts/sec constantly, corresponding to screen refresh rate).
As far as the bus mastering activity detection, the kernel just gets this data from the hardware, it has no control over what kind of transfers are reported as bus mastering or not. However, if the VBlank interrupt processing is resulting in bus master activity, it would explain it.