linux-kernel - Re: [PATCH v7 06/10] trace: Add lock-free tracing

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Date:	Fri, 12 Jun 2015 14:17:31 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Tom Zanussi <tom.zanussi@...ux.intel.com>
Cc:	daniel.wagner@...-carit.de, masami.hiramatsu.pt@...achi.com,
	namhyung@...nel.org, josh@...htriplett.org, andi@...stfloor.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 06/10] trace: Add lock-free tracing_map

On Mon,  8 Jun 2015 16:32:05 -0500
Tom Zanussi <tom.zanussi@...ux.intel.com> wrote:

> Add tracing_map, a special-purpose lock-free map for tracing.
> 
> tracing_map is designed to aggregate or 'sum' one or more values
> associated with a specific object of type tracing_map_elt, which

What is "elt"? I don't see it explained anywhere.


> is associated by the map to a given key.
> 
> It provides various hooks allowing per-tracer customization and is
> separated out into a separate file in order to allow it to be shared
> between multiple tracers, but isn't meant to be generally used outside
> of that context.
> 
> The tracing_map implementation was inspired by lock-free map
> algorithms originated by Dr. Cliff Click:
> 
>  http://www.azulsystems.com/blog/cliff/2007-03-26-non-blocking-hashtable
>  http://www.azulsystems.com/events/javaone_2007/2007_LockFreeHash.pdf
> 
> Signed-off-by: Tom Zanussi <tom.zanussi@...ux.intel.com>


> +/**
> + * tracing_map_update_sum - Add a value to a tracing_map_elt's sum
> + * @elt: The tracing_map_elt

Not a very useful comment, as I have no idea what "elt" is.

I'll continue to review this patch about the mysterious element "elt".

-- Steve

> + * @i: The index of the given sum associated with the tracing_map_elt
> + * @n: The value to add to the sum
> + *
> + * Add n to sum i associated with the specified tracing_map_elt
> + * instance.  The index i is the index returned by the call to
> + * tracing_map_add_sum_field() when the tracing map was set up.
> + */
> +void tracing_map_update_sum(struct tracing_map_elt *elt, unsigned int i, u64 n)
> +{
> +	atomic64_add(n, &elt->fields[i].sum);
> +}
> +

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