Eliminating tasklets

Posted Jun 29, 2007 21:15 UTC (Fri) by giraffedata (subscriber, #1954) [Link]

But note that the latency that gets improved is the latency of processing interrupts, not the latency of anything a process does. When you consider that a tasklet can't sleep and runs before the CPU returns to regular process stuff, and limit your view to single CPU systems, it isn't as clear that rescheduling interrupt handling for a different time helps any latency. A program that gets interrupted still is not going to get control back until all that interrupt processing is done.

Here's the latency that gets improved: Consider 10 interrupts of the same class that happen one after another. The first 9 take 1ms to service and nobody's urgently waiting for the result. #10 only takes a microsecond, and if you don't respond within 1ms, expensive hardware will go idle. Without tasklets, those interrupts get serviced in order of arrival, so expensive hardware will be idle for 8 ms. With tasklets, you make the code for 1-9 reschedule their work to tasklets (only takes a microsecond to reschedule) and #10 completes in 10 microseconds, soon enough to keep the expensive hardware busy.