Re: [PATCH v7 1/2]: perf util: map data buffer for preserving collected data

[Jiri Olsa <jolsa@redhat.com>]

On Wed, Sep 05, 2018 at 10:19:56AM +0300, Alexey Budankov wrote:
> 
> The map->data buffers are used to preserve map->base profiling data 
> for writing to disk. AIO map->cblocks are used to queue corresponding 
> map->data buffers for asynchronous writing. map->cblocks objects are 
> located in the last page of every map->data buffer.
> 
> Signed-off-by: Alexey Budankov <alexey.budankov@linux.intel.com>
> ---
>  Changes in v7:
>   - implemented handling record.aio setting from perfconfig file
>  Changes in v6:
>   - adjusted setting of priorities for cblocks;
>  Changes in v5:
>   - reshaped layout of data structures;
>   - implemented --aio option;
>  Changes in v4:
>   - converted mmap()/munmap() to malloc()/free() for mmap->data buffer management 
>  Changes in v2:
>   - converted zalloc() to calloc() for allocation of mmap_aio array,
>   - cleared typo and adjusted fallback branch code;
> ---
>  tools/perf/builtin-record.c | 15 ++++++++++++-
>  tools/perf/perf.h           |  1 +
>  tools/perf/util/evlist.c    |  7 +++---
>  tools/perf/util/evlist.h    |  3 ++-
>  tools/perf/util/mmap.c      | 53 +++++++++++++++++++++++++++++++++++++++++++++
>  tools/perf/util/mmap.h      |  6 ++++-
>  6 files changed, 79 insertions(+), 6 deletions(-)
> 
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index 22ebeb92ac51..f17a6f9cb1ba 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -326,7 +326,8 @@ static int record__mmap_evlist(struct record *rec,
>  
>  	if (perf_evlist__mmap_ex(evlist, opts->mmap_pages,
>  				 opts->auxtrace_mmap_pages,
> -				 opts->auxtrace_snapshot_mode) < 0) {
> +				 opts->auxtrace_snapshot_mode,
> +				 opts->nr_cblocks) < 0) {
>  		if (errno == EPERM) {
>  			pr_err("Permission error mapping pages.\n"
>  			       "Consider increasing "
> @@ -1287,6 +1288,8 @@ static int perf_record_config(const char *var, const char *value, void *cb)
>  		var = "call-graph.record-mode";
>  		return perf_default_config(var, value, cb);
>  	}
> +	if (!strcmp(var, "record.aio"))
> +		rec->opts.nr_cblocks = strtol(value, NULL, 0);
>  
>  	return 0;
>  }
> @@ -1519,6 +1522,7 @@ static struct record record = {
>  			.default_per_cpu = true,
>  		},
>  		.proc_map_timeout     = 500,
> +		.nr_cblocks	      = 2
>  	},
>  	.tool = {
>  		.sample		= process_sample_event,
> @@ -1678,6 +1682,8 @@ static struct option __record_options[] = {
>  			  "signal"),
>  	OPT_BOOLEAN(0, "dry-run", &dry_run,
>  		    "Parse options then exit"),
> +	OPT_INTEGER(0, "aio", &record.opts.nr_cblocks,
> +		    "asynchronous trace write operations (min: 1, max: 32, default: 2)"),

ok, so this got silently added in recent versions and I couldn't
find any justification for it.. why do we use more aio blocks for
single map now? also why the default is 2?

the option should be more specific like 'aio-blocks'

the change is difficult enough.. we should start simple and add
these additions with proper justification in separate patches

thanks,
jirka