On Mon, Oct 26, 2009 at 11:13:18PM +0800, Wu Zhangjin wrote: > trace_clock_local() is based on the arch-specific sched_clock(), in X86, > it is tsc(64bit) based, which can give very high precision(about 1ns > with 1GHz). but in MIPS, the sched_clock() is jiffies based, which can > give only 10ms precison with 1000 HZ. which is not enough for tracing, > especially for Real Time system. > > so, we need to implement a MIPS specific sched_clock() to get higher > precision. There is a tsc like clock counter register in MIPS, whose > frequency is half of the processor, so, if the cpu frequency is 800MHz, > the time precision reaches 2.5ns, which is very good for tracing, even > for Real Time system. > > but 'Cause it is only 32bit long, which will rollover quickly, so, such > a sched_clock() will bring with extra load, which is not good for the > whole system. so, we only need to implement a arch-specific > trace_clock_local() for tracing. as a preparation, we convert it as a > weak function. > > The MIPS specific trace_clock_local() is coming in the next two patches. > > Signed-off-by: Wu Zhangjin <wuzhangjin@xxxxxxxxx> Yep, if trace_clock_local() had to be a strict alias to sched_clock(), we would have simply used sched_clock(). If an arch need to implement it another way, then yeah making it weak is a good thing. Acked-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
