RE: [EXT] [PATCH v2 5/9] trace: fix dynamically enabling trace points

[Sunil Kumar Kori <skori@marvell.com>]

> -----Original Message-----
> From: David Marchand <david.marchand@redhat.com>
> Sent: Tuesday, October 4, 2022 3:14 PM
> To: dev@dpdk.org
> Cc: skori@mavell.com; Jerin Jacob Kollanukkaran <jerinj@marvell.com>;
> stable@dpdk.org; Sunil Kumar Kori <skori@marvell.com>
> Subject: [EXT] [PATCH v2 5/9] trace: fix dynamically enabling trace points
> 
> External Email
> 
> ----------------------------------------------------------------------
> Enabling trace points at runtime was not working if no trace point had been
> enabled first at rte_eal_init() time. The reason was that trace.args reflected
> the arguments passed to --trace= EAL option.
> 
> To fix this:
> - the trace subsystem initialisation is updated: trace directory
>   creation is deferred to when traces are dumped (to avoid creating
>   directories that may not be used),
> - per lcore memory allocation still relies on rte_trace_is_enabled() but
>   this helper now tracks if any trace point is enabled. The
>   documentation is updated accordingly,
> - cleanup helpers must always be called in rte_eal_cleanup() since some
>   trace points might have been enabled and disabled in the lifetime of
>   the DPDK application,
> 
> With this fix, we can update the unit test and check that a trace point callback
> is invoked when expected.
> 
> Note:
> - the 'trace' global variable might be shadowed with the argument
>   passed to the functions dealing with trace point handles.
>   'tp' has been used for referring to trace_point object.
>   Prefer 't' for referring to handles,
> 
> Fixes: 84c4fae4628f ("trace: implement operation APIs")
> Cc: stable@dpdk.org
> 
> Signed-off-by: David Marchand <david.marchand@redhat.com>
> ---
> Changes since v1:
> - restored level to INFO for trace directory log message,
> - moved trace_mkdir() to rte_trace_save,
> 
> ---
>  app/test/test_trace.c                   | 20 ++++++++++
>  app/test/test_trace.h                   |  2 +
>  doc/guides/prog_guide/trace_lib.rst     | 14 +++++--
>  lib/eal/common/eal_common_trace.c       | 53 ++++++++++---------------
>  lib/eal/common/eal_common_trace_utils.c | 11 ++++-
>  lib/eal/common/eal_trace.h              |  3 +-
>  6 files changed, 65 insertions(+), 38 deletions(-)
> 

[snip]

> diff --git a/lib/eal/common/eal_common_trace_utils.c
> b/lib/eal/common/eal_common_trace_utils.c
> index 2b55dbec65..7bf1c05e12 100644
> --- a/lib/eal/common/eal_common_trace_utils.c
> +++ b/lib/eal/common/eal_common_trace_utils.c
> @@ -314,14 +314,18 @@ trace_dir_default_path_get(char *dir_path)
>  	return 0;
>  }
> 
> -int
> +static int
>  trace_mkdir(void)
>  {
>  	struct trace *trace = trace_obj_get();
>  	char session[TRACE_DIR_STR_LEN];
> +	static bool already_done;
>  	char *dir_path;
>  	int rc;
> 
> +	if (already_done)
> +		return 0;
> +

As trace_mkdir() call is being moved to rte_trace_save() so there won't be another context which will be invoking trace_mkdir().
So is this logic still needed here ?

>  	if (!trace->dir_offset) {
>  		dir_path = calloc(1, sizeof(trace->dir));
>  		if (dir_path == NULL) {
> @@ -365,6 +369,7 @@ trace_mkdir(void)
>  	}
> 
>  	RTE_LOG(INFO, EAL, "Trace dir: %s\n", trace->dir);
> +	already_done = true;
>  	return 0;
>  }
> 
> @@ -434,6 +439,10 @@ rte_trace_save(void)
>  	if (trace->nb_trace_mem_list == 0)
>  		return rc;
> 
> +	rc = trace_mkdir();
> +	if (rc < 0)
> +		return rc;
> +
>  	rc = trace_meta_save(trace);
>  	if (rc)
>  		return rc;

[snip]

> 2.37.3