Messages in this thread | | | Subject | Re: [PATCH v7 03/17] tracing: add MIPS specific trace_clock_local() | From | Wu Zhangjin <> | Date | Wed, 11 Nov 2009 10:47:16 +0800 |
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Hi,
On Tue, 2009-11-10 at 09:48 -0800, David Daney wrote: > Wu Zhangjin wrote: > [...] > > + * trace_clock_local(): the simplest and least coherent tracing clock. > > + * > > + * Useful for tracing that does not cross to other CPUs nor > > + * does it go through idle events. > > + */ > > +u64 trace_clock_local(void) > > +{ > > + unsigned long flags; > > + u64 clock; > > + > > + raw_local_irq_save(flags); > > + > > + clock = mips_timecounter_read(); > > + > > + raw_local_irq_restore(flags); > > + > > + return clock; > > +} > > Why disable interrupts? >
I got it from kernel/trace/trace_clock.c:
/* * trace_clock_local(): the simplest and least coherent tracing clock. * * Useful for tracing that does not cross to other CPUs nor * does it go through idle events. */ u64 notrace trace_clock_local(void) { unsigned long flags; u64 clock;
/* * sched_clock() is an architecture implemented, fast, scalable, * lockless clock. It is not guaranteed to be coherent across * CPUs, nor across CPU idle events. */ raw_local_irq_save(flags); clock = sched_clock(); raw_local_irq_restore(flags);
return clock; }
> Also you call the new function mips_timecounter_read(). Since > sched_clock() is a weak function, you can override the definition with a > more accurate version when possible. Then you could just directly call > it here, instead of adding the new mips_timecounter_read() that the > '[PATCH v7 02/17] tracing: add mips_timecounter_read() for MIPS' adds. >
Yes, I have tried to override the sched_clock(), but failed on booting(just hang there). and also, as you know, this version of mips_timecounter_read() will bring us some overhead, I think it's not a good idea to enable it for the whole system, so, I only enable it for ftrace.
Regards, Wu Zhangjin
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