linux-kernel - Re: [PATCH 1/7] trace: Move trace_seq

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Date:   Wed, 15 Mar 2017 20:54:20 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Andi Kleen <andi@...stfloor.org>
Cc:     akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 1/7] trace: Move trace_seq_overflowed out of line

On Tue, 14 Mar 2017 19:14:25 -0700
Andi Kleen <andi@...stfloor.org> wrote:

> From: Andi Kleen <ak@...ux.intel.com>
> 
> Inlining trace_seq_overflowed takes ~17k in text size in my kernel.
> The function doesn't seem to be time critical, so we can just out of line it.

Instead of out of lining trace_seq_has_overflowed(), have you tried to
out of line the function that's called by tracepoints (one per
tracepoint). That is, trace_handle_return()?

The trace_seq_handle_overflow() is used in not reproduced places that I
would like to keep it as an inline. If the issue is size of the kernel,
please just out of line the one place that calls it that is duplicated
for every tracepoint. Which happens to be trace_handle_return().

Thanks!

-- Steve


> 
> Function                                           Total          Avg   Num
> trace_seq_has_overflowed                           17134 (0.00%)  33    514
> 
> This saves around 6k here
> 
>    text    data     bss     dec     hex filename
> 9102881 5367568 11116544        25586993        1866d31 vmlinux-orig
> 9096494 5367568 11116544        25580606        186543e vmlinux-trace-seq
> 
> Cc: rostedt@...dmis.org
> Signed-off-by: Andi Kleen <ak@...ux.intel.com>
> ---
>  include/linux/trace_seq.h | 12 +-----------
>  kernel/trace/trace_seq.c  | 15 +++++++++++++++
>  2 files changed, 16 insertions(+), 11 deletions(-)
> 
> diff --git a/include/linux/trace_seq.h b/include/linux/trace_seq.h
> index cfaf5a1d4bad..442e4f087b95 100644
> --- a/include/linux/trace_seq.h
> +++ b/include/linux/trace_seq.h
> @@ -56,17 +56,7 @@ trace_seq_buffer_ptr(struct trace_seq *s)
>  	return s->buffer + seq_buf_used(&s->seq);
>  }
>  
> -/**
> - * trace_seq_has_overflowed - return true if the trace_seq took too much
> - * @s: trace sequence descriptor
> - *
> - * Returns true if too much data was added to the trace_seq and it is
> - * now full and will not take anymore.
> - */
> -static inline bool trace_seq_has_overflowed(struct trace_seq *s)
> -{
> -	return s->full || seq_buf_has_overflowed(&s->seq);
> -}
> +bool trace_seq_has_overflowed(struct trace_seq *s);
>  
>  /*
>   * Currently only defined when tracing is enabled.
> diff --git a/kernel/trace/trace_seq.c b/kernel/trace/trace_seq.c
> index e694c9f9efa4..4367cd43e38c 100644
> --- a/kernel/trace/trace_seq.c
> +++ b/kernel/trace/trace_seq.c
> @@ -375,3 +375,18 @@ int trace_seq_to_user(struct trace_seq *s, char __user *ubuf, int cnt)
>  	return seq_buf_to_user(&s->seq, ubuf, cnt);
>  }
>  EXPORT_SYMBOL_GPL(trace_seq_to_user);
> +
> +
> +
> +/**
> + * trace_seq_has_overflowed - return true if the trace_seq took too much
> + * @s: trace sequence descriptor
> + *
> + * Returns true if too much data was added to the trace_seq and it is
> + * now full and will not take anymore.
> + */
> +bool trace_seq_has_overflowed(struct trace_seq *s)
> +{
> +	return s->full || seq_buf_has_overflowed(&s->seq);
> +}
> +EXPORT_SYMBOL_GPL(trace_seq_has_overflowed);