On 17 December 2013 22:05, Kevin Hilman khilman@linaro.org wrote:
For future reference, for generating email friendly trace output for discussion like this, you can use something like:
trace-cmd report --cpu=1 trace.dat
Okay..
And after that the next event comes after 5 Seconds.
And so I was talking for the Event 41.
That first event (Event 41) is an interrupt, and comes from the scheduler tick. The tick is happening because the writeback workqueue just ran and we're not in NO_HZ mode.
This is what I was trying to ask. Why can't we enter in NO_HZ_FULL mode as soon as writeback workqueue just ran? That way we can go into NOHZ mode earlier..
However, as soon as that IRQ (and resulting softirqs) are finished, we enter NO_HZ mode again. But as you mention, it only lasts for ~5 sec when the timer fires again. Once again, it fires because of the writeback workqueue, and soon therafter it switches back to NO_HZ mode again.
That's fine.. It wasn't part of my query :) .. But yes your trick would be useful for my usecase :)