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

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Message-ID: <1A7043D5F58CCB44A599DFD55ED4C9484688EFD5@fmsmsx115.amr.corp.intel.com>
Date:	Tue, 26 May 2015 00:32:39 +0000
From:	"Brown, Len" <len.brown@...el.com>
To:	Prarit Bhargava <prarit@...hat.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()



> -----Original Message-----
> From: Prarit Bhargava [mailto:prarit@...hat.com]
> Sent: Friday, May 22, 2015 6:30 PM
> To: Brown, Len
> Cc: linux-kernel@...r.kernel.org; linux-pm@...r.kernel.org; Semin, Andrey
> 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");

Agreed, that is better than invoking the syscall directly,
as we already are using the sched.h interface in this code.

thanks,
-Len

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