linux-kernel - Re: [PATCH v2 36/40] tracing: Remove lookups from tracing

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Date:   Tue, 12 Sep 2017 11:16:11 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Tom Zanussi <tom.zanussi@...ux.intel.com>
Cc:     rostedt@...dmis.org, tglx@...utronix.de, mhiramat@...nel.org,
        namhyung@...nel.org, vedang.patel@...el.com, bigeasy@...utronix.de,
        joel.opensrc@...il.com, joelaf@...gle.com,
        mathieu.desnoyers@...icios.com, baohong.liu@...el.com,
        linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org
Subject: Re: [PATCH v2 36/40] tracing: Remove lookups from tracing_map
 hitcount

Hi Tom,

On Tue,  5 Sep 2017 16:57:48 -0500
Tom Zanussi <tom.zanussi@...ux.intel.com> wrote:

> Lookups inflate the hitcount, making it essentially useless.  Only
> inserts and updates should really affect the hitcount anyway, so
> explicitly filter lookups out.
> 
> Signed-off-by: Tom Zanussi <tom.zanussi@...ux.intel.com>
> ---
>  kernel/trace/tracing_map.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/tracing_map.c b/kernel/trace/tracing_map.c
> index a4e5a56..f8e2338 100644
> --- a/kernel/trace/tracing_map.c
> +++ b/kernel/trace/tracing_map.c
> @@ -538,7 +538,8 @@ static inline bool keys_match(void *key, void *test_key, unsigned key_size)
>  		if (test_key && test_key == key_hash) {
>  			if (entry->val &&
>  			    keys_match(key, entry->val->key, map->key_size)) {
> -				atomic64_inc(&map->hits);
> +				if (!lookup_only)
> +					atomic64_inc(&map->hits);

Is this a kind of bugfix for current code?
If so, such patch can be posted in separate series.

Thank you,

>  				return entry->val;
>  			} else if (unlikely(!entry->val)) {
>  				/*
> -- 
> 1.9.3
> 


-- 
Masami Hiramatsu <mhiramat@...nel.org>