linux-kernel - Re: [PATCH 2/2] turbostat, add set_base

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Message-ID: <555FADFA.609@redhat.com>
Date:	Fri, 22 May 2015 18:30:18 -0400
From:	Prarit Bhargava <prarit@...hat.com>
To:	"Brown, Len" <len.brown@...el.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"Semin, Andrey" <andrey.semin@...el.com>
Subject: Re: [PATCH 2/2] turbostat, add set_base_cpu()



On 05/22/2015 11:55 AM, Brown, Len wrote:
>> +void set_base_cpu(void)
>> +{
>> +	int cpu;
>> +
>> +	for (cpu = 0; cpu <= topo.max_cpu_num; ++cpu) {
>> +		if (cpu_is_not_present(cpu))
>> +			continue;
>> +		base_cpu = cpu;
>> +		break;
>> +	}
>> +
>> +	if (base_cpu == -1)
>> +		err(-ENODEV, "No valid cpus found");
>> +}
> 
> 
> cpu0 hard-coding is indeed arbitrary.
> However, so is this proposed replacement, base_cpu.
> Either may not match where turbostat is currently running,
> and thus could provoke unnecessary cross-calls to get there.
> 
> I think it would be better to ask getcpu(2) where we are already running,
> and simply use that one.  I think we can call it once and cache it,
> as you proposed, rather than multiple system calls.

Any objection to sched_getcpu()?  That way the code is simply

	base_cpu = sched_getcpu();

	if (base_cpu == -1)
		err(-ENODEV, "No valid cpus found");

P.

> 
> thanks,
> -Len
> 
> ps. patches to turbostat should go to linux-pm@...r.kernel.org
> 
> 
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