Messages in this thread | | | Date | Sat, 29 Aug 2009 12:21:01 +0200 | From | Frederic Weisbecker <> | Subject | Re: [PATCH 2/3] tracing: block-able ring_buffer consumer |
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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.
> + 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.
> } > > /* > 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.
> + > + /* > + * 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.
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