Messages in this thread | | | Date | Tue, 01 Sep 2009 20:53:03 +0800 | From | Lai Jiangshan <> | Subject | Re: [PATCH 2/3] tracing: block-able ring_buffer consumer |
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Frederic Weisbecker wrote: > On Thu, Aug 27, 2009 at 11:03:04AM +0800, Lai Jiangshan wrote: >> makes consumer side(per_cpu/cpu#/trace_pipe_raw) block-able, >> which is a TODO in trace.c >> >> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> >> --- >> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h >> index dc3b132..b5dcf34 100644 >> --- a/include/linux/ftrace.h >> +++ b/include/linux/ftrace.h >> @@ -512,4 +512,10 @@ static inline void trace_hw_branch_oops(void) {} >> >> #endif /* CONFIG_HW_BRANCH_TRACER */ >> >> +#ifdef CONFIG_TRACING >> +void tracing_notify(void); >> +#else >> +static inline void tracing_notify(void) {} >> +#endif >> + >> #endif /* _LINUX_FTRACE_H */ >> diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h >> index 7fca716..b81ceed 100644 >> --- a/include/linux/ring_buffer.h >> +++ b/include/linux/ring_buffer.h >> @@ -185,6 +185,10 @@ void ring_buffer_free_read_page(struct ring_buffer *buffer, void *data); >> int ring_buffer_read_page(struct ring_buffer *buffer, void **data_page, >> size_t len, int cpu, int full); >> >> +void ring_buffer_notify(struct ring_buffer *buffer); >> +signed long ring_buffer_wait_page(struct ring_buffer *buffer, int cpu, > > > No need to use signed, it's implicit in the long type.
Ouch, I tried my best to make it returns the same type as schedule_timeout() returns and forgot "long" == "signed long"
> > > >> + signed long timeout); >> + >> struct trace_seq; >> >> int ring_buffer_print_entry_header(struct trace_seq *s); >> diff --git a/kernel/timer.c b/kernel/timer.c >> index 6e712df..79f5596 100644 >> --- a/kernel/timer.c >> +++ b/kernel/timer.c >> @@ -39,6 +39,7 @@ >> #include <linux/kallsyms.h> >> #include <linux/perf_counter.h> >> #include <linux/sched.h> >> +#include <linux/ftrace.h> >> >> #include <asm/uaccess.h> >> #include <asm/unistd.h> >> @@ -1178,6 +1179,7 @@ void update_process_times(int user_tick) >> printk_tick(); >> scheduler_tick(); >> run_posix_cpu_timers(p); >> + tracing_notify(); > > > > Hmm, that looks really not a good idea. The tracing shouldn't ever impact > the system when it is inactive. > Especially in such a fast path like the timer interrupt.
It do nothing at most time. It just calls tracing_notify() and then returns, but... it still has several mb()s, I can remove this mb()s in next patch.
We cannot call wake_up() and the tracing write side, so we delay the wake_up() until next timer interrupt.
> > > >> } >> >> /* >> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c >> index f1e1533..db82b38 100644 >> --- a/kernel/trace/ring_buffer.c >> +++ b/kernel/trace/ring_buffer.c >> @@ -443,6 +443,7 @@ struct ring_buffer_per_cpu { >> u64 write_stamp; >> u64 read_stamp; >> atomic_t record_disabled; >> + wait_queue_head_t sleepers; > > > That seems a too generic name. May be consumer_queue? > > >> }; >> >> struct ring_buffer { >> @@ -999,6 +999,7 @@ rb_allocate_cpu_buffer(struct ring_buffer *buffer, int cpu) >> spin_lock_init(&cpu_buffer->reader_lock); >> lockdep_set_class(&cpu_buffer->reader_lock, buffer->reader_lock_key); >> cpu_buffer->lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED; >> + init_waitqueue_head(&cpu_buffer->sleepers); >> >> bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()), >> GFP_KERNEL, cpu_to_node(cpu)); >> @@ -3318,6 +3319,77 @@ ring_buffer_read(struct ring_buffer_iter *iter, u64 *ts) >> EXPORT_SYMBOL_GPL(ring_buffer_read); >> >> /** >> + * ring_buffer_notify - notify the sleepers when there is any available page >> + * @buffer: The ring buffer. >> + */ >> +void ring_buffer_notify(struct ring_buffer *buffer) >> +{ >> + unsigned long flags; >> + struct ring_buffer_per_cpu *cpu_buffer; >> + >> + cpu_buffer = buffer->buffers[smp_processor_id()]; >> + >> + if (!spin_trylock_irqsave(&cpu_buffer->reader_lock, flags)) >> + return; >> + >> + if (waitqueue_active(&cpu_buffer->sleepers)) { >> + struct buffer_page *reader_page; >> + struct buffer_page *commit_page; >> + >> + reader_page = cpu_buffer->reader_page; >> + commit_page = ACCESS_ONCE(cpu_buffer->commit_page); > > > ACCESS_ONCE makes sense if you loop, to ensure the value > is not cached through iteration, but there I'm not sure this is > useful. >
commit_page is used twice here, It needs to be loaded only once.
> > >> + >> + /* >> + * ring_buffer_notify() is fast path, so we don't use the slow >> + * rb_get_reader_page(cpu_buffer, 1) to detect available pages. >> + */ >> + if (reader_page == commit_page) >> + goto out; >> + >> + if (reader_page->read < rb_page_commit(reader_page) >> + || rb_set_head_page(cpu_buffer) != commit_page) > > > > This may need a small comment to explain you are checking that the reader > is not completely consumed. > >
Yes, it needs.
Thank a lot.
Lai.
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