On Fri, 2009-10-16 at 19:52 +0800, Américo Wang wrote: > On Fri, Oct 16, 2009 at 07:38:24PM +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 patch. > > > >Signed-off-by: Wu Zhangjin <wuzhangjin@xxxxxxxxx> > >--- > > kernel/trace/trace_clock.c | 2 +- > > 1 files changed, 1 insertions(+), 1 deletions(-) > > > >diff --git a/kernel/trace/trace_clock.c b/kernel/trace/trace_clock.c > >index 20c5f92..a04dc18 100644 > >--- a/kernel/trace/trace_clock.c > >+++ b/kernel/trace/trace_clock.c > >@@ -26,7 +26,7 @@ > > * Useful for tracing that does not cross to other CPUs nor > > * does it go through idle events. > > */ > >-u64 notrace trace_clock_local(void) > >+u64 __attribute__((weak)) notrace trace_clock_local(void) > > We have __weak. > Thanks, will use it in the next version. Regards, Wu Zhangjin
