Re: [PATCH] perf stat: Add hint for SMI cost measurement

Ingo Molnar
2019-04-25T06:39:16Z

* kan.liang@linux.intel.com <kan.liang@linux.intel.com> wrote:

> +static void smi_env_check(void)
> +{
> + char *name;
> + size_t len;
> +
> + if (sysfs__read_str(CPUIDLE_CUR_DRV, &name, &len)) {
> + pr_warning("Failed to check cstate status.\n");

What a meaningless message. What did we want to do, what happened, and
why did it fail?

> + return;
> + }
> +
> + if (strncmp(name, "none", 4)) {
> + pr_warning("Cstate may cause drift between aperf and cycles. "
> + "Please completely disable cstate, "
> + "E.g. set idle=poll in grub\n");

Please keep user-visible strings in the same form that the user sees
them, i.e. in a single line.

By doing that you'll also note a capitalization error.

Also what does 'Cstate may cause drift' mean? What aspect of cstates
causes the drift - entering/exiting deeper cstates that are not C0? If so
then say so.

Thanks,

Ingo