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

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Date:   Thu, 25 Apr 2019 09:14:00 -0400
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Ingo Molnar <mingo@...nel.org>
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



On 4/25/2019 2:39 AM, Ingo Molnar wrote:
> 
> * 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.

To avoid the line over 80 characters, the quoted string was split across 
lines in the code. But the string is shown as a single line when it is 
output for user.

Are you suggesting to ignore the 80 characters rule when printing 
user-visible strings?
Could you please confirm?

Thanks,
Kan

> 
> 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
>