linux-kernel - Re: [PATCH V4 2/2] perf/x86: add sysfs entry to freeze counter on SMI

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Message-ID: <20170329062459.GA1460@gmail.com>
Date:   Wed, 29 Mar 2017 08:24:59 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     kan.liang@...el.com
Cc:     peterz@...radead.org, tglx@...utronix.de, mingo@...hat.com,
        linux-kernel@...r.kernel.org, bp@...en8.de, acme@...nel.org,
        eranian@...gle.com, jolsa@...nel.org, ak@...ux.intel.com
Subject: Re: [PATCH V4 2/2] perf/x86: add sysfs entry to freeze counter on SMI

* kan.liang@...el.com <kan.liang@...el.com> wrote:

> +static void flip_smm_bit(void *data)
> +{
> +	int val = *(int *)data;
> +
> +	msr_flip_bit(MSR_IA32_DEBUGCTLMSR, DEBUGCTLMSR_FREEZE_WHILE_SMM_BIT, (bool)val);
> +}

BTW., you can probably shorten that and remove a type cast by using a more natural 
type for 'val':

static void flip_smm_bit(void *data)
{
	bool set = *(int *)data;

	msr_flip_bit(MSR_IA32_DEBUGCTLMSR, DEBUGCTLMSR_FREEZE_WHILE_SMM_BIT, set);
}

Also note that 'set' is the more natural local variable name here as well, as it 
matches the parameter name of the msr_flip_bit() function.

BTW. #2, "MSR_IA32_DEBUGCTLMSR" is a bit of a misnomer, why is 'MSR' mentioned 
twice? If it was 'MSR_IA32_DEBUGCTL' then it could all be:

	msr_flip_bit(MSR_IA32_DEBUGCTL, DEBUGCTL_FREEZE_WHILE_SMM_BIT, set);

plus if 'FREEZE_WHILE_SMM' is renamed to 'FREEZE_IN_SMM', we'd have:

	msr_flip_bit(MSR_IA32_DEBUGCTL, DEBUGCTL_FREEZE_IN_SMM_BIT, set);

... which, incidentally, fits into 80 cols nicely.

But that's unrelated to your patch, you just made canonical use of the existing 
nomenclature.

Thanks,

	Ingo