RE: [PATCH 2/2] turbostat, add set_base_cpu()

From: "Brown, Len" <len.brown@intel.com>
To: Prarit Bhargava <prarit@redhat.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>
Cc: "Semin, Andrey" <andrey.semin@intel.com>
Subject: RE: [PATCH 2/2] turbostat, add set_base_cpu()
Date: Fri, 22 May 2015 15:55:15 +0000	[thread overview]
Message-ID: <1A7043D5F58CCB44A599DFD55ED4C9484688E5F2@fmsmsx115.amr.corp.intel.com> (raw)
In-Reply-To: <1432296063-22185-3-git-send-email-prarit@redhat.com>

> +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.

thanks,
-Len

ps. patches to turbostat should go to linux-pm@vger.kernel.org