linux-kernel - Re: [PATCH] x86/perf/intel/cqm: Get rid of the silly for_each

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Message-ID: <alpine.DEB.2.10.1602171036450.3157@vshiva-Udesk>
Date:	Wed, 17 Feb 2016 10:48:18 -0800 (PST)
From:	Vikas Shivappa <vikas.shivappa@...el.com>
To:	Thomas Gleixner <tglx@...utronix.de>
cc:	Vikas Shivappa <vikas.shivappa@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
	Stephane Eranian <eranian@...gle.com>,
	Matt Fleming <matt@...eblueprint.co.uk>
Subject: Re: [PATCH] x86/perf/intel/cqm: Get rid of the silly for_each_cpu
 lookups



On Wed, 17 Feb 2016, Thomas Gleixner wrote:

> On Wed, 17 Feb 2016, Vikas Shivappa wrote:
>
> Yes, please resend the rapl one. perf_uncore is a different trainwreck which I
> fixed already:
>
>      lkml.kernel.org/r/20160217132903.767990400@...utronix.de

Ok , will resend the rapl separately.

the fix i sent however was a little different in that it uses a static 
tmp_cpumask to avoid the loop in the cpumask_and_any below -
         while ((n = cpumask_next(n, src1p)) < nr_cpu_ids)
                 if (cpumask_test_cpu(n, src2p))

But we have an extra static - static to avoid having it in the 
stack..

copy below -

+/*
+ * Temporary cpumask used during hot cpu notificaiton handling. The usage
+ * is serialized by hot cpu locks.
+ */
+static cpumask_t tmp_cpumask;
+

  static void rapl_cpu_init(int cpu)
  {
-       int i, phys_id = topology_physical_package_id(cpu);
-
-       /* check if phys_is is already covered */
-       for_each_cpu(i, &rapl_cpu_mask) {
-               if (phys_id == topology_physical_package_id(i))
-                       return;
-       }
-       /* was not found, so add it */
-       cpumask_set_cpu(cpu, &rapl_cpu_mask);
+       /* check if cpu's package is already covered.If not, add it.*/
+       cpumask_and(&tmp_cpumask, &rapl_cpu_mask, topology_core_cpumask(cpu));
+       if (cpumask_empty(&tmp_cpumask))
+               cpumask_set_cpu(cpu, &rapl_cpu_mask);
  }

Thanks,
Vikas

>
> Thanks,
>
> 	tglx
>