Re: [PATCH] tools/power/turbostat: fix compatibility with older kernels

[Borislav Petkov <bp@suse.de>]

On Wed, Jan 27, 2021 at 03:24:44PM +0200, Artem Bityutskiy wrote:
> From: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
> 
> Commit
> 
> 6d6501d912a9 tools/power/turbostat: Read energy_perf_bias from sysfs
> 
> added a useful EPB print by reading EPB from sysfs's 'energy_perf_bias' file.
> However, older kernels, which do not necessarily have that sysfs file (e.g.,
> Centos 7's stock kernel does not have it). As a result, turbostat fails with
> older kernels.
> 
> This patch fixes the problem by ignoring the sysfs file read errors.
> 
> Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
> ---
>  tools/power/x86/turbostat/turbostat.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/power/x86/turbostat/turbostat.c b/tools/power/x86/turbostat/turbostat.c
> index 389ea5209a83..12e014f2c24b 100644
> --- a/tools/power/x86/turbostat/turbostat.c
> +++ b/tools/power/x86/turbostat/turbostat.c
> @@ -1839,7 +1839,9 @@ int get_epb(int cpu)
>  
>  	sprintf(path, "/sys/devices/system/cpu/cpu%d/power/energy_perf_bias", cpu);
>  
> -	fp = fopen_or_die(path, "r");
> +	fp = fopen(path, "r");
> +	if (!fp)
> +		return -1;
>  
>  	ret = fscanf(fp, "%d", &epb);
>  	if (ret != 1)

So I was under the impression that things in tools/ are tied to the
kernel version they're shipped with. Which means, you should probably
get the one from the centos kernel.

However, if this is supposed to work on older kernels too, then

  6d6501d912a9 ("tools/power/turbostat: Read energy_perf_bias from sysfs")

would need to be extended to first test the sysfs file's existence and
if not there, fall back to the MSR reading...

-- 
Regards/Gruss,
    Boris.

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