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Message-ID: <CAHN2JJ8WmyPPnVyJJxFg-OFJwrb9c6VuG5bUhkM82hjd3nwU4g@mail.gmail.com>
Date: Tue, 29 Apr 2014 15:09:15 -0700
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
Subject: Re: [PATCH v2] tracing: Allow changing default ring buffer size for
ftrace instances.
We'd actually considered doing just that, in an initial version of the patch.
At the time, we'd decided in favour of allowing the user more explicit
control over the buffer size, rather than auto expanding it. (The
discussion on that is here:
https://lkml.org/lkml/2013/7/1/617)
We could go back to that though if you think that's okay, but I think
your previous reasoning still makes sense: it's useful for the user to
know if there will be an allocation failure before enabling tracing.
What are your thoughts?
Bharath Ravi | rbharath@...gle.com
On Fri, Apr 25, 2014 at 10:52 AM, Steven Rostedt <rostedt@...dmis.org> wrote:
> On Fri, 14 Feb 2014 15:29:57 -0800
> Bharath Ravi <rbharath@...gle.com> wrote:
>
>> Hi Steven,
>>
>> Does this version of the patch look reasonable?
>
> Sorry, your email got buried in my TODO list :-/
>
> Anyway, what about if we make new instances act like the original
> buffer does on start up? That is, have it start out as a minimum buffer
> with an "expanded" attribute.
>
> # cd /sys/kernel/debug/tracing/instances
> # mkdir foo
> # cd foo
> # cat buffer_size_kb
> 7 (expanded: 1408)
> # echo 1 > events/enable
> # cat buffer_size_kb
> 1408
>
> This way if you don't want to waste a lot of buffer size when creating
> a new instance, you can simply change the size after creation.
>
> How's that sound?
>
> -- Steve
>
>
>> --
>> 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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