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

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Message-ID: <20190425063910.GA85646@gmail.com>
Date:   Thu, 25 Apr 2019 08:39:10 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     kan.liang@...ux.intel.com
Cc:     acme@...hat.com, mingo@...hat.com, linux-kernel@...r.kernel.org,
        jolsa@...hat.com, namhyung@...il.com, lgoncalv@...hat.com,
        ak@...ux.intel.com
Subject: Re: [PATCH] perf stat: Add hint for SMI cost measurement

* kan.liang@...ux.intel.com <kan.liang@...ux.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