Messages in this thread Patch in this message | | | Date | Fri, 1 May 2009 05:08:49 +0200 | From | Frederic Weisbecker <> | Subject | Re: [PATCH 2/3] tracing: export stats of ring buffers to userspace |
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On Thu, Apr 30, 2009 at 10:22:12PM -0400, Steven Rostedt wrote: > From: Steven Rostedt <srostedt@redhat.com> > > This patch adds stats to the ftrace ring buffers: > > # cat /debugfs/tracing/per_cpu/cpu0/stats > entries: 42360 > overrun: 30509326 > commit overrun: 0 > nmi dropped: 0 > > Where entries are the total number of data entries in the buffer. > > overrun is the number of entries not consumed and were overwritten by > the writer. > > commit overrun is the number of entries dropped due to nested writers > wrapping the buffer before the initial writer finished the commit.
I feel a bit confused with this one. How such a thing can happen? The write page and the commit page are not the same. So is that because we can have (ring-buffer inspires all of us to try ascii-art):
Write page Commit page (which becomes new write page) ------------------------------------ ----------------- | | | | | Writer 1 | Writer 2 | Writer n | | Writer n + 1 | ..... reserved | reserved | reserved | | reserved | ----------------------------------- ---------------- | ^ | | ---------------- Was supposed to commit here--|
I know this is silly, my picture seem to show a data copy whereas the ring buffer deals with page pointers. But the commit page on the ring buffer is a mistery for me. Just because you haven't drawn in in ascii in your comments :)
Thanks. Frederic.
> nmi dropped is the number of entries dropped due to the ring buffer > lock being held when an nmi was going to write to the ring buffer. > Note, this field will be meaningless and will go away when the ring > buffer becomes lockless. > > [ Impact: let userspace know what is happening in the ring buffers ] > > Signed-off-by: Steven Rostedt <rostedt@goodmis.org> > --- > kernel/trace/trace.c | 42 ++++++++++++++++++++++++++++++++++++++++++ > 1 files changed, 42 insertions(+), 0 deletions(-) > > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > index f5427e0..74df029 100644 > --- a/kernel/trace/trace.c > +++ b/kernel/trace/trace.c > @@ -3595,6 +3595,45 @@ static const struct file_operations tracing_buffers_fops = { > .llseek = no_llseek, > }; > > +static ssize_t > +tracing_stats_read(struct file *filp, char __user *ubuf, > + size_t count, loff_t *ppos) > +{ > + unsigned long cpu = (unsigned long)filp->private_data; > + struct trace_array *tr = &global_trace; > + struct trace_seq *s; > + unsigned long cnt; > + > + s = kmalloc(sizeof(*s), GFP_ATOMIC); > + if (!s) > + return ENOMEM; > + > + trace_seq_init(s); > + > + cnt = ring_buffer_entries_cpu(tr->buffer, cpu); > + trace_seq_printf(s, "entries: %ld\n", cnt); > + > + cnt = ring_buffer_overrun_cpu(tr->buffer, cpu); > + trace_seq_printf(s, "overrun: %ld\n", cnt); > + > + cnt = ring_buffer_commit_overrun_cpu(tr->buffer, cpu); > + trace_seq_printf(s, "commit overrun: %ld\n", cnt); > + > + cnt = ring_buffer_nmi_dropped_cpu(tr->buffer, cpu); > + trace_seq_printf(s, "nmi dropped: %ld\n", cnt); > + > + count = simple_read_from_buffer(ubuf, count, ppos, s->buffer, s->len); > + > + kfree(s); > + > + return count; > +} > + > +static const struct file_operations tracing_stats_fops = { > + .open = tracing_open_generic, > + .read = tracing_stats_read, > +}; > + > #ifdef CONFIG_DYNAMIC_FTRACE > > int __weak ftrace_arch_read_dyn_info(char *buf, int size) > @@ -3708,6 +3747,9 @@ static void tracing_init_debugfs_percpu(long cpu) > > trace_create_file("trace_pipe_raw", 0444, d_cpu, > (void *) cpu, &tracing_buffers_fops); > + > + trace_create_file("stats", 0444, d_cpu, > + (void *) cpu, &tracing_stats_fops); > } > > #ifdef CONFIG_FTRACE_SELFTEST > -- > 1.6.2.1 > > --
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