linux-kernel - Re: [PATCH v2] tracing: Allow changing default ring buffer size for ftrace instances.

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Date:	Fri, 14 Feb 2014 15:29:57 -0800
From:	Bharath Ravi <rbharath@...gle.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Vaibhav Nagarnaik <vnagarnaik@...gle.com>,
	David Sharp <dhsharp@...gle.com>,
	Laurent Chavey <chavey@...gle.com>,
	linux-kernel@...r.kernel.org, Bharath Ravi <rbharath@...gle.com>
Subject: Re: [PATCH v2] tracing: Allow changing default ring buffer size for
 ftrace instances.

Hi Steven,

Does this version of the patch look reasonable?
--
Bharath Ravi |  rbharath@...gle.com


On Thu, Jan 23, 2014 at 11:37 AM, Bharath Ravi <rbharath@...gle.com> wrote:
>
> It is often memory efficient to start instances off with a smaller ring
> buffer size than the current default. This is particularly true on
> systems with many cores, or when multiple ftrace instances are created,
> where the current (higher) default value results in allocation failures.
>
> The global trace buffer allows initialization with a minimal (1 byte)
> size, to save memory using a "ring_buffer_expanded" flag. To allow
> instances a similar capability, trace option named "expand-new-buffers"
> is added. If set to true, ftrace instances created will be initialized
> with ring buffers of the default size. If set to false, the buffers will
> be initialized with a size of 1 byte. By default, the expand_new_buffers
> flag is true.
>
> Tested: Booted into a kernel with these changes, verified reading and
> writing the new trace_option. Ensured that new ftrace instances created
> used the appropriate size while initializing their ring buffers.
>
> Signed-off-by: Bharath Ravi <rbharath@...gle.com>
> ---
>  kernel/trace/trace.c | 13 ++++++++++---
>  kernel/trace/trace.h |  1 +
>  2 files changed, 11 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 9d20cd9..c17c12f 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -410,7 +410,8 @@ static inline void trace_access_lock_init(void)
>  unsigned long trace_flags = TRACE_ITER_PRINT_PARENT | TRACE_ITER_PRINTK |
>         TRACE_ITER_ANNOTATE | TRACE_ITER_CONTEXT_INFO | TRACE_ITER_SLEEP_TIME |
>         TRACE_ITER_GRAPH_TIME | TRACE_ITER_RECORD_CMD | TRACE_ITER_OVERWRITE |
> -       TRACE_ITER_IRQ_INFO | TRACE_ITER_MARKERS | TRACE_ITER_FUNCTION;
> +       TRACE_ITER_IRQ_INFO | TRACE_ITER_MARKERS | TRACE_ITER_FUNCTION |
> +       TRACE_EXPAND_NEW_BUFFERS;
>
>  static void tracer_tracing_on(struct trace_array *tr)
>  {
> @@ -753,6 +754,7 @@ static const char *trace_options[] = {
>         "irq-info",
>         "markers",
>         "function-trace",
> +       "expand-new-buffers",
>         NULL
>  };
>
> @@ -5930,7 +5932,7 @@ static int allocate_trace_buffers(struct trace_array *tr, int size)
>  static int new_instance_create(const char *name)
>  {
>         struct trace_array *tr;
> -       int ret;
> +       int ret, ring_buffer_size;
>
>         mutex_lock(&trace_types_lock);
>
> @@ -5961,7 +5963,12 @@ static int new_instance_create(const char *name)
>         INIT_LIST_HEAD(&tr->systems);
>         INIT_LIST_HEAD(&tr->events);
>
> -       if (allocate_trace_buffers(tr, trace_buf_size) < 0)
> +       /* allocate memory only if buffers are to be expanded */
> +       if (trace_flags & TRACE_EXPAND_NEW_BUFFERS)
> +               ring_buffer_size = trace_buf_size;
> +       else
> +               ring_buffer_size = 1
> +       if (allocate_trace_buffers(tr, ring_buffer_size) < 0)
>                 goto out_free_tr;
>
>         tr->dir = debugfs_create_dir(name, trace_instance_dir);
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index ea189e0..15ddbf4 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -888,6 +888,7 @@ enum trace_iterator_flags {
>         TRACE_ITER_IRQ_INFO             = 0x800000,
>         TRACE_ITER_MARKERS              = 0x1000000,
>         TRACE_ITER_FUNCTION             = 0x2000000,
> +       TRACE_EXPAND_NEW_BUFFERS        = 0x4000000,
>  };
>
>  /*
> --
> 1.8.5.3
>
--
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