On 02/25/2010 05:06 PM, Paul Brook wrote:
Idle bottom halves (i.e. qemu_bh_schedule_idle) are just bugs waiting to
happen, and should never be used for anything.
Idle bottom halves make considerable more sense than the normal bottom
halves.
The fact that rescheduling a bottom half within a bottom half results in
an infinite loop is absurd. It is equally absurd that bottoms halves
alter the select timeout. The result of that is that if a bottom half
schedules another bottom half, and that bottom half schedules the
previous, you get a tight infinite loop. Since bottom halves are used
often times deep within functions, the result is very subtle infinite
loops (that we've absolutely encountered in the past).
I disagree. The "select timeout" is a completely irrelevant implementation
detail. Anything that relies on it is just plain wrong. If you require a delay
then you should be using a timer. If scheduling a BH directly then you should
expect it to be processed without delay.
I agree. Further, once we fine-grain device threading, the iothread
essentially disappears and is replaced by device-specific threads.
There's no "idle" anymore.
--
Do not meddle in the internals of kernels, for they are subtle and quick to
panic.
