linux-kernel - Re: [RFC PATCH 5/7] perf tools: Support setting different slots in a BPF map separately

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Date:	Fri, 20 Nov 2015 21:25:36 +0800
From:	"Wangnan (F)" <wangnan0@...wei.com>
To:	<acme@...nel.org>, <ast@...mgrid.com>, <brendan.d.gregg@...il.com>
CC:	<a.p.zijlstra@...llo.nl>, <daniel@...earbox.net>,
	<dsahern@...il.com>, <hekuang@...wei.com>, <jolsa@...nel.org>,
	<lizefan@...wei.com>, <masami.hiramatsu.pt@...achi.com>,
	<namhyung@...nel.org>, <paulus@...ba.org>,
	<linux-kernel@...r.kernel.org>, <pi3orama@....com>,
	<xiakaixu@...wei.com>, Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [RFC PATCH 5/7] perf tools: Support setting different slots in
 a BPF map separately



On 2015/10/17 18:48, Wang Nan wrote:
> This patch introduces basic facilities to support config different
> slots in a BPF map one by one.
>
> nr_indics and indics are introduced into 'struct parse_events_term',
> where indics is an array of indics which will be configured by this
> config term, nr_indics is the size of the array. The array is passed
> to 'struct bpf_map_priv'. To indicate the new type of configuration,
> BPF_MAP_PRIV_KEY_INDICS is added as a new key type.
> bpf_map_config_foreach_key() is extended to iterate over those indics
> instead of all possible keys.
>
> Signed-off-by: Wang Nan <wangnan0@...wei.com>
> Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
> Cc: Alexei Starovoitov <ast@...mgrid.com>
> Cc: Brendan Gregg <brendan.d.gregg@...il.com>
> Cc: Daniel Borkmann <daniel@...earbox.net>
> Cc: David Ahern <dsahern@...il.com>
> Cc: He Kuang <hekuang@...wei.com>
> Cc: Jiri Olsa <jolsa@...nel.org>
> Cc: Kaixu Xia <xiakaixu@...wei.com>
> Cc: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> Cc: Namhyung Kim <namhyung@...nel.org>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Cc: Zefan Li <lizefan@...wei.com>
> Cc: pi3orama@....com
> ---
>   tools/perf/util/bpf-loader.c   | 68 +++++++++++++++++++++++++++++++++++++++++-
>   tools/perf/util/parse-events.c |  4 ++-
>   tools/perf/util/parse-events.h |  2 ++
>   3 files changed, 72 insertions(+), 2 deletions(-)
>
> diff --git a/tools/perf/util/bpf-loader.c b/tools/perf/util/bpf-loader.c
> index 15cf27a..023fc12 100644
> --- a/tools/perf/util/bpf-loader.c
> +++ b/tools/perf/util/bpf-loader.c
> @@ -638,6 +638,7 @@ int bpf__foreach_tev(struct bpf_object *obj,
>   
>   enum bpf_map_priv_key_type {
>   	BPF_MAP_PRIV_KEY_ALL,
> +	BPF_MAP_PRIV_KEY_INDICS,
>   };
>   
>   enum bpf_map_priv_value_type {
> @@ -647,6 +648,12 @@ enum bpf_map_priv_value_type {
>   struct bpf_map_priv {
>   	struct {
>   		enum bpf_map_priv_key_type type;
> +		union {
> +			struct {
> +				size_t nr_indics;
> +				u64 *indics;
> +			} indics;
> +		};
>   	} key;
>   
>   	struct {
> @@ -663,6 +670,8 @@ bpf_map_priv__clear(struct bpf_map *map __maybe_unused,
>   {
>   	struct bpf_map_priv *priv = _priv;
>   
> +	if (priv->key.type == BPF_MAP_PRIV_KEY_INDICS)
> +		zfree(&priv->key.indics.indics);
>   	free(priv);
>   }
>   
> @@ -718,6 +727,20 @@ bpf_map_config_foreach_key(struct bpf_map *map,
>   				}
>   			}
>   			return 0;
> +		case BPF_MAP_PRIV_KEY_INDICS:
> +			for (i = 0; i < priv->key.indics.nr_indics; i++) {
> +				u64 _idx = priv->key.indics.indics[i];
> +				unsigned int idx = (unsigned int)(_idx);
> +
> +				err = (*func)(name, map_fd, &def,
> +					      priv, &idx, arg);
> +				if (err) {
> +					pr_debug("ERROR: failed to insert value to %s[%u]\n",
> +						 name, idx);
> +					return err;
> +				}
> +			}

This for-loop has a potential problem that, if perf's user want to
set a very big array using indices, for example:

  # perf record -e 
mybpf.c/maps:mymap:values[1,2,3,10-100000,200000-400000]=3/ 
mybpf.c/maps:mymap:values[100000-200000]=3/ ...

Perf would alloc nearly 300000 slots for indices array, consume too much 
memory.

I will fix this problem by reinterprete indices array, makes negative
value represent range start and use next slot to store range size. For
example, the above perf cmdline can be converted to:

{1,2,3,-10, 99991,-200000,200001} and {-100000,100001}.

Thank you.

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