On 15 April 2014 14:43, Frederic Weisbecker <fweis...@gmail.com> wrote: > Yeah. But not just that. > > Using an inline saves a function call and reduce the offline case to a simple > condition check. But there is also the jump label that reduce the condition > check > to an unconditional jump in the off case. > > To summarize, here's how calling tick_nohz_task_switch() maps to final C code: > > finish_task_switch() > { > //do things before calling tick_nohz_task_switch()... > // call tick_nohz_task_switch > goto offcase; > if (tick_nohz_full_enabled()) > __tick_nohz_task_switch(tsk); > offcase: > //end of call to tick_nohz_task_switch > //do things before calling tick_nohz_task_switch()... > } > > In the offcase, the code is like above. We don't even do the check, thanks to > the jump label code we unconditionally jump to what's next in > finish_task_switch() > (there is actually nothing afterward but that's for the picture). > > Now if there is at least a CPU that is full dynticks on boot, it is enabled > with context_tracking_cpu_set(). Then the jump label code patches the code in > finish_task_switch() to turn the goto offcase into a nop. Then the condition > is > actually verified on every call to finish_task_switch(). > > So it goes beyond than just saving a function call.
Sorry, but my poor mind still couldn't understand what you are trying to tell me :( So lets clarify things one by one :) - What do you mean by offcase? CONFIG_NO_HZ_FULL not configured into the kernel or it is configured but none of the CPUs is running in that mode? - Also what does it correspond to in code: goto offcase; ? There is no labels or goto statements in code that I can see.. This is how the code looks to me. > finish_task_switch() > { > //do things before calling tick_nohz_task_switch()... > // call tick_nohz_task_switch > if (tick_nohz_full_enabled()) > __tick_nohz_task_switch(tsk); > } __tick_nohz_task_switch() may or maynot be available at all depending on CONFIG_NO_HZ_FULL is enabled into the kernel or not. But that was the case with tick_nohz_task_switch() as well in my patch. So shouldn't make a difference.. Again, sorry for not understanding what you are trying to explain here. I want to understand this once and for all and probably add a comment here as well :) -- viresh -- 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/