linux-kernel - Re: [PATCH 4/5 v3] tracing/core: drop the old ftrace_printk implementation in favour of ftrace

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Date:	Fri, 6 Mar 2009 11:49:40 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 4/5 v3] tracing/core: drop the old ftrace_printk
 implementation in favour of ftrace_bprintk



On Fri, 6 Mar 2009, Frederic Weisbecker wrote:

> Impact: faster and lighter tracing
> 
> Now that we have ftrace_bprintk() which is faster and consume lesser
> memory than ftrace_printk() and has the same purpose, we can now drop
> the old implementation in favour of the binary one from ftrace_bprintk(),
> which means we move all the implementation of ftrace_bprintk() to
> ftrace_printk(), so the Api doesn't change except that we must now use
> trace_seq_bprintk() to print the TRACE_PRINT entries.
> 
> Some changes result of this:
> 
> - Previously, ftrace_bprintk depended of a single tracer and couldn't
>   work without. This tracer has been dropped and the whole implementation
>   of ftrace_printk() (like the module formats management) is now integrated
>   in the tracing core (comes with CONFIG_TRACING), though we keep the file
>   trace_printk (previously trace_bprintk.c) where we can find the module
>   management. Thus we don't overflow trace.c
> 
> - changes some parts to use trace_seq_bprintk() to print TRACE_PRINT entries.
> 
> - change a bit ftrace_printk/ftrace_vprintk macros to support non-builtin formats
>   constants, and fix 'const' qualifiers warnings. But this is all transparent for
>   developers.
> 
> - etc...
> 
> V2:
> 
> - Rebase against last changes
> - Fix mispell on the changelog
> 
> V3:
> 
> - Rebase against last changes (moving ftrace_printk() to kernel.h)
> 
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>

Very nice Frederic!

For some reason I'm still missing patch 1. Perhaps it decided to take the
scenic route ;-)

> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index 0f5077f..6140922 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -20,7 +20,6 @@ enum trace_type {
>  	TRACE_WAKE,
>  	TRACE_STACK,
>  	TRACE_PRINT,
> -	TRACE_BPRINTK,
>  	TRACE_SPECIAL,
>  	TRACE_MMIO_RW,
>  	TRACE_MMIO_MAP,
> @@ -120,16 +119,10 @@ struct userstack_entry {
>   */
>  struct print_entry {
>  	struct trace_entry	ent;
> -	unsigned long		ip;
> +	unsigned long 		ip;
>  	int			depth;
> -	char			buf[];
> -};
> -


Note, this is going to break my recent patch that exports the internal 
ftrace events. That's OK, I'll fix it after Ingo pulls it in.

Ingo,

Would you prefer that I pull these patches in and then fix the code, and 
let you pull it from me?

-- Steve

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