On Mon, 9 Mar 2009, Steven Rostedt wrote:
>
> On Mon, 9 Mar 2009, Ingo Molnar wrote:
> >
> > tracing: optimize trace_printk()
> >
> > Impact: micro-optimization
> >
> > trace_printk() does this unconditionally:
> >
> > trace_printk_fmt = fmt;
> >
> > Where trace_printk_fmt is an entry into a global array. This is
> > very SMP-unfriendly.
> >
> > So only write it once per bootup.
> >
> > Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
> > Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > LKML-Reference: <1236356510-8381-5-git-send-email-fweisbec@xxxxxxxxx>
> > Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
> >
> >
> > ---
> > include/linux/kernel.h | 10 ++++++++--
> > 1 files changed, 8 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> > index 4e726b9..7742798 100644
> > --- a/include/linux/kernel.h
> > +++ b/include/linux/kernel.h
> > @@ -454,7 +454,10 @@ do { \
> > do { \
> > static const char *trace_printk_fmt \
> > __attribute__((section("__trace_printk_fmt"))); \
A I missed the semicolon. I wonder if we could make it a static init?
-- Steve
> > - trace_printk_fmt = fmt; \
> > + \
> > + if (!trace_printk_fmt) \
> > + trace_printk_fmt = fmt; \
> > + \
>
> But this is a static init. That is, it is done at initialization and not
> every time.
>
> The change actually slows down the system.
>
> > __trace_printk_check_format(fmt, ##args); \
> > __trace_printk(_THIS_IP_, trace_printk_fmt, ##args); \
> > } while (0)
> > @@ -467,7 +470,10 @@ __trace_printk(unsigned long ip, const char *fmt, ...)
> > do { \
> > static const char *trace_printk_fmt \
> > __attribute__((section("__trace_printk_fmt"))); \
> > - trace_printk_fmt = fmt; \
> > + \
> > + if (!trace_printk_fmt) \
> > + trace_printk_fmt = fmt; \
> > + \
>
> Same here.
>
> -- Steve
>
> > __ftrace_vprintk(_THIS_IP_, trace_printk_fmt, vargs); \
> > } while (0)
> >
> >
>
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