Until now, when the poll_loop module's log level was turned up to "debug",
it would log a backtrace of the call stack for the event that caused poll()
to wake up in poll_block(). This was pretty useful from time to time to
find out why ovs-vswitchd was using more CPU than expected, because we
could find out what was causing it to wake up.
But there were some issues. One is simply that the backtrace was printed
as a series of hexadecimal numbers, so GDB or another debugger was needed
to translate it into human-readable format. Compiler optimizations meant
that even the human-readable backtrace wasn't, in my experience, as helpful
as it could have been. And, of course, one needed to have the binary to
interpret the backtrace. When the backtrace couldn't be interpreted or
wasn't meaningful, there was essentially nothing to fall back on.
This commit changes the way that "debug" logging for poll_block() wakeups
works. Instead of logging a backtrace, it logs the source code file name
and line number of the call to a poll_loop function, using __FILE__ and
__LINE__. This is by itself much more meaningful than a sequence of
hexadecimal numbers, since no additional interpretation is necessary. It
can be useful even if the Open vSwitch version is only approximately known.
In addition to the file and line, this commit adds, for wakeups caused by
file descriptors, information about the file descriptor itself: what kind
of file it is (regular file, directory, socket, etc.), the name of the file
(on Linux only), and the local and remote endpoints for socket file
descriptors.
Here are a few examples of the new output format:
932-ms timeout at ../ofproto/in-band.c:507
[POLLIN] on fd 20 (192.168.0.20:35388<->192.168.0.3:6633) at ../lib/stream-fd.c:149
[POLLIN] on fd 7 (FIFO pipe:[48049]) at ../lib/fatal-signal.c:168
Every so often I get concerned because OVS does most of its time arithmetic
in "long long int" but poll_timer_wait() takes an "int", so there is
potential for truncating a large value to a small value or a positive value
to a negative value. That would cause excessive wakeups and possibly 100%
CPU usage.
This commit therefore changes poll_timer_wait()'s parameter type from "int"
to "long long int". The file-scope 'timeout' variable remains type "int"
because that is the type of poll()'s timeout argument.
Factoring poll_timer_wait() into two functions is not necessary here but it
comes in handy in the following patch.
The last user of this feature has been removed, so delete the feature too,
simplifying poll-loop.c significantly.
poll_cancel() is no longer used, either, but deleting it is much less
beneficial.
