linux-kernel - Re: [PATCH v9 08/22] tracing: Add 'hist' event trigger command

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Message-ID: <55ACF98A.9070307@hitachi.com>
Date:	Mon, 20 Jul 2015 22:37:14 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Tom Zanussi <tom.zanussi@...ux.intel.com>, rostedt@...dmis.org
CC:	daniel.wagner@...-carit.de, namhyung@...nel.org,
	josh@...htriplett.org, andi@...stfloor.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v9 08/22] tracing: Add 'hist' event trigger command

Hi Tom,

On 2015/07/17 2:22, Tom Zanussi wrote:

> @@ -3782,6 +3785,32 @@ static const char readme_msg[] =
>  	"\t   To remove a trigger with a count:\n"
>  	"\t     echo '!<trigger>:0 > <system>/<event>/trigger\n"
>  	"\t   Filters can be ignored when removing a trigger.\n"
> +#ifdef CONFIG_HIST_TRIGGERS
> +	"      hist trigger\t- If set, event hits are aggregated into a hash table\n"
> +	"\t    Format: hist:keys=<field1>\n"
> +	"\t            [:size=#entries]\n"
> +	"\t            [if <filter>]\n\n"
> +	"\t    When a matching event is hit, an entry is added to a hash\n"
> +	"\t    table using the key named.  Keys correspond to fields in the\n"
> +	"\t    event's format description.  On an event hit, the value of a\n"
> +	"\t    sum called 'hitcount' is incremented, which is simply a count\n"
> +	"\t    of event hits.  Keys can be any field.\n\n"
> +	"\t    Reading the 'hist' file for the event will dump the hash\n"
> +	"\t    table in its entirety to stdout.  Each printed hash table\n"
> +	"\t    entry is a simple list of the keys and values comprising the\n"
> +	"\t    entry; keys are printed first and are delineated by curly\n"
> +	"\t    braces, and are followed by the set of value fields for the\n"
> +	"\t    entry.  Numeric fields are displayed as base-10 integers.\n"
> +	"\t    By default, the size of the hash table is 2048 entries.  The\n"
> +	"\t    'size' param can be used to specify more or fewer than that.\n"
> +	"\t    The units are in terms of hashtable entries - if a run uses\n"
> +	"\t    more entries than specified, the results will show the number\n"
> +	"\t    of 'drops', the number of hits that were ignored.  The size\n"
> +	"\t    should be a power of 2 between 128 and 131072 (any non-\n"
> +	"\t    power-of-2 number specified will be rounded up).\n\n"
> +	"\t    The entries are sorted by 'hitcount' and the sort order is\n"
> +	"\t    'ascending'.\n\n"


Hmm, this seems too much about implementation of histogram. Could you shorten this
to be a half ?


Thank you,


-- 
Masami HIRAMATSU
Linux Technology Research Center, System Productivity Research Dept.
Center for Technology Innovation - Systems Engineering
Hitachi, Ltd., Research & Development Group
E-mail: masami.hiramatsu.pt@...achi.com
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