Messages in this thread | | | Date | Mon, 08 Jul 2013 22:46:04 +0300 | From | Eliezer Tamir <> | Subject | Re: [PATCH net-next] net: rename low latency sockets functions to busy poll |
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On 08/07/2013 22:37, Linus Torvalds wrote: > On Mon, Jul 8, 2013 at 10:14 AM, Eliezer Tamir > <eliezer.tamir@linux.intel.com> wrote: >> >> I think there is no way for the compiler to know the value of >> can_busy_loop at compile time. It depends on the replies we get >> from polling the sockets. ll_flag was there to make sure the compiler >> will know when things are defined out. > > No, my point was that we want to handle the easily seen register test > first, and not even have to load current(). > > The compiler may end up scheduling the code to load current anyway, > but the way you wrote it it's pretty much guaranteed that it will do > it.
I see. OK.
> In fact, I'd argue for initializing start_time to zero, and have the > "have we timed out" logic load it only if necessary, rather than > initializing it based on whether POLL_BUSY_WAIT was set or not. > Because one common case - even with POLL_BUSY_WAIT - is that we go > through the loop exactly once, and the data exists on the very first > try. And that is in fact the case we want to optimize and not do any > extra work for at all. > > So I would actually argue that the whole timeout code might as well be > something like > > unsigned long start_time = 0; > ... > if (want_busy_poll && !need_resched()) { > unsigned long now = busy_poll_sched_clock(); > if (!start_time) { > start_time = now + sysctl.busypoll; > continue; > } > if (time_before(start_time, now)) > continue; > } >
OK.
Thanks, Eliezer
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