Messages in this thread | | | Date | Thu, 1 Jul 2010 20:48:59 +0900 | Subject | Re: [PATCH v2] tracing: shrink max latency ringbuffer if unnecessary | From | KOSAKI Motohiro <> |
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2010/7/1 Lai Jiangshan <laijs@cn.fujitsu.com>: > KOSAKI Motohiro wrote: >> >> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> >> --- >> kernel/trace/trace.c | 39 ++++++++++++++++++++++++++++++------ >> kernel/trace/trace.h | 1 + >> kernel/trace/trace_irqsoff.c | 3 ++ >> kernel/trace/trace_sched_wakeup.c | 2 + >> 4 files changed, 38 insertions(+), 7 deletions(-) >> > > Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com > > >> - >> + if (current_trace && current_trace->use_max_tr) { >> + /* >> + * We don't free the ring buffer. instead, resize it because >> + * The max_tr ring buffer has some state (e.g. ring->clock) and >> + * we want preserve it. >> + */ >> + ring_buffer_resize(max_tr.buffer, 1); >> + max_tr.entries = 1; >> + } >> destroy_trace_option_files(topts); >> >> current_trace = t; >> >> topts = create_trace_option_files(current_trace); > > I think we can skip the two resize when current_trace->use_max_tr==1 && t->use_max_tr==1
Yup. but I don't think it's worthful because it's rarely operation.
> >> + if (current_trace->use_max_tr) { >> + ret = ring_buffer_resize(max_tr.buffer, global_trace.entries); >> + if (ret < 0) >> + goto out; >> + max_tr.entries = global_trace.entries; >> + } >> >> if (t->init) { >> ret = tracer_init(t, tr); > > Does we need to shrink it when tracer_init() fails? > Although tracer_init() hardly fails, and there is no bad effect even we don't shrink it.
Nope. brief code of tracing_set_tracer() is here
======================================== if (current_trace && current_trace->reset) current_trace->reset(tr);
destroy_trace_option_files(topts);
current_trace = t;
topts = create_trace_option_files(current_trace);
if (t->init) { ret = tracer_init(t, tr); if (ret) goto out; } ========================================
That's mean, if t->init fail, we can't rollback old tracer. so your suggested micro optimization doesn't makes observable improvement, I think.
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