linux-kernel - Re: [PATCH] perf: Do not require /lib/modules/* on a guest

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Message-ID: <51F6EF7A.4000209@gmail.com>
Date:	Mon, 29 Jul 2013 16:40:58 -0600
From:	David Ahern <dsahern@...il.com>
To:	Jason Wessel <jason.wessel@...driver.com>, acme@...stprotocols.net
CC:	a.p.zijlstra@...llo.nl, paulus@...ba.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf: Do not require /lib/modules/* on a guest

On 7/15/13 2:27 PM, Jason Wessel wrote:
> For some types of work loads and special guest environments, you might
> have a kernel that has no kernel modules.  The perf kvm record tool
> fails instantiate vmlinux maps when the kernel modules directory
> cannot be opened, even though the kallsyms has been properly
> processed.  This leads to a perf kvm report that has no guest symbols
> resolved.

Theoretically, use of modules is an option:

     if (symbol_conf.use_modules && machine__create_modules(machine) < 0) {
...
     }

But, the use_modules option was flipped from false to true by b32d133a 
back in 2009. And the lack of complaints suggests this ominous warning 
in perf-report, diff and annotate is moot:

     OPT_BOOLEAN('m', "modules", &symbol_conf.use_modules,
             "load module symbols - WARNING: use only with -k and LIVE 
kernel"),

>
> This patch changes the failure to locate kernel modules to be
> non-fatal.
>
> Signed-off-by: Jason Wessel <jason.wessel@...driver.com>
> ---
>   tools/perf/util/machine.c |    5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
> index b2ecad6..eb9ebd6 100644
> --- a/tools/perf/util/machine.c
> +++ b/tools/perf/util/machine.c
> @@ -808,7 +808,10 @@ static int machine__create_modules(struct machine *machine)
>   	free(line);
>   	fclose(file);
>
> -	return machine__set_modules_path(machine);
> +	if (machine__set_modules_path(machine) < 0) {
> +		pr_debug("Problems setting modules path maps, continuing anyway...\n");
> +	}
> +	return 0;
>
>   out_delete_line:
>   	free(line);

Acked-by: David Ahern <dsahern@...il.com>

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