From: Frederic Weisbecker <fweisbec@gmail.com>
To: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Steven Rostedt <rostedt@goodmis.org>,
linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 5/6] tracing: reduce latency and remove percpu trace_seq
Date: Sat, 30 Jan 2010 22:24:11 +0100 [thread overview]
Message-ID: <20100130212410.GI5675@nowhere> (raw)
In-Reply-To: <4B5E5C59.2080203@cn.fujitsu.com>
On Tue, Jan 26, 2010 at 11:07:05AM +0800, Lai Jiangshan wrote:
> Frederic Weisbecker wrote:
> > On Tue, Jan 19, 2010 at 03:34:22PM +0800, Lai Jiangshan wrote:
> >> __print_flags() and __print_symbolic() use percpu trace_seq:
> >>
> >> 1) Its memory is preallocated, it wastes memory when we don't use tracing.
> >> 2) It wastes memory for multi-cpus system.
> >> 3) It disables preemption when it executes its core routine
> >> "trace_seq_printf(s, "%s: ", #call);" and introduce latency
> >> for more important process.
> >>
> >> So we move this trace_seq to struct trace_iterator.
> >>
> >> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
> >> ---
> >> diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
> >> index be9ece5..348500d 100644
> >> --- a/include/linux/ftrace_event.h
> >> +++ b/include/linux/ftrace_event.h
> >> @@ -12,9 +12,6 @@ struct dentry;
> >>
> >> #define FTRACE_SEQ_BUFSIZE PAGE_SIZE
> >>
> >> -DECLARE_PER_CPU(struct trace_seq, ftrace_event_seq);
> >> -DECLARE_PER_CPU(unsigned char[FTRACE_SEQ_BUFSIZE], ftrace_event_buffer);
> >> -
> >> struct trace_print_flags {
> >> unsigned long mask;
> >> const char *name;
> >> @@ -60,6 +57,10 @@ struct trace_iterator {
> >> struct trace_seq seq;
> >> unsigned char buffer[FTRACE_SEQ_BUFSIZE];
> >>
> >> + /* trace_seq for __print_flags() and __print_symbolic() */
> >> + struct trace_seq tmp_seq;
> >> + unsigned char tmp_buffer[FTRACE_SEQ_BUFSIZE];
> >
> >
> >
> >
> > Well, I don't like much that because it's a temporary buffer
> > in trace iter only used by few events.
> > But the problem is indeed tricky.
> >
> > May be should we use a kmalloc in raw_output?
> >
>
> But we have to preallocate it before raw_output().
> a kmalloc in raw_output make ftrace_dump() unhappy.
Ah, right.
>
> At real system, tracepoints are used more frequently,
> So it is not "only used by few events."
No I mean, print_flags and print_symbolic are used by few
events.
> But maybe FTRACE_SEQ_BUFSIZE is too large, 128 is enough.
May be. Anyway, we should perhaps indeed make this change.
Steve?
prev parent reply other threads:[~2010-01-30 21:24 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-01-19 7:34 [PATCH 5/6] tracing: reduce latency and remove percpu trace_seq Lai Jiangshan
2010-01-20 19:22 ` Frederic Weisbecker
2010-01-26 3:07 ` Lai Jiangshan
2010-01-30 21:24 ` Frederic Weisbecker [this message]
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