On Thu, Oct 17, 2013 at 05:40:38PM +0100, Morten Rasmussen wrote: > On Mon, Oct 14, 2013 at 04:14:25PM +0100, Arjan van de Ven wrote: > > On 10/14/2013 6:33 AM, Peter Zijlstra wrote: > > > On Fri, Oct 11, 2013 at 06:19:14PM +0100, Morten Rasmussen wrote: > > >> Removing power hints for kworker threads enables easier use of > > >> workqueues in the power driver late callback. That would otherwise > > >> lead to an endless loop unless it is prevented in the power driver. > > > > > > There's many kworker users; some of them actually consume lots of > > > cputime. Therefore how did you come to the conclusion that excepting all > > > users was the better choice of a little added complexity in the one > > > place where it actually matters? > > > > .. and likely only for a very few architectures > > > > x86, and I suspect modern ARM, can change frequency synchronously. > > (using an instruction or maybe two or three for ARM) > > It should be possible to implement synchronous frequency changes on most > modern ARM platforms. It is a bit more than a few instructions to change > frequency though particularly for the current cpufreq drivers. > > cpufreq drivers, like the one for ARM TC2, uses the clock framework to > manage clocks. clk_set_rate() is allowed to sleep which won't work if we > call it from scheduler context. The clock framework will need a look if > it doesn't provide a very fast synchronous alternative to clk_set_rate() > to change frequency and we want to use it for scheduler driven frequency > scaling. > > cpufreq has pre- and post-change notifiers so the current TC2 clock driver > waits (yields) in its clk_set_rate() implementation until the change has > happened to ensure that the post-change notifier happens at the right > time. Since clk_set_rate() is allowed to sleep other tasks may be > running while waiting for the change to complete. This may be true for > other clock drivers as well. > > AFAICT, there is no way to reuse the existing cpufreq drivers in a > sensible way for scheduler driven frequency scaling. It should be > possible to have very fast frequency changes on ARM but it is not the > way it is currently done.
Note that you still have preemption disabled in your late callback from finish_task_switch(). There's no way you can wait/yield/whatever from there. Nor is that really sane. Just say no to the existing cruft ? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
