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Date: Tue, 11 May 2010 01:09:13 +0200
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Lin Ming <ming.m.lin@intel.com>, Ingo Molnar <mingo@elte.hu>,
       "eranian@gmail.com" <eranian@gmail.com>,
       "Gary.Mohr@Bull.com" <Gary.Mohr@bull.com>,
       Corey Ashford <cjashfor@linux.vnet.ibm.com>,
       "arjan@linux.intel.com" <arjan@linux.intel.com>,
       "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>,
       Paul Mackerras <paulus@samba.org>,
       "David S. Miller" <davem@davemloft.net>,
       Russell King <rmk+kernel@arm.linux.org.uk>,
       Paul Mundt <lethal@linux-sh.org>, lkml <linux-kernel@vger.kernel.org>
Subject: Re: [RFC][PATCH 2/9] perf: core, remove hw_perf_event_init
Message-ID: <20100510230911.GB5895@nowhere>
References: <1273483595.15998.56.camel@minggr.sh.intel.com> <1273484430.5605.3334.camel@twins> <1273486670.15998.80.camel@minggr.sh.intel.com> <1273486769.5605.3343.camel@twins> <20100510122728.GB5563@nowhere> <1273496054.5605.3400.camel@twins>
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On Mon, May 10, 2010 at 02:54:14PM +0200, Peter Zijlstra wrote:
> On Mon, 2010-05-10 at 14:27 +0200, Frederic Weisbecker wrote:
> > On Mon, May 10, 2010 at 12:19:29PM +0200, Peter Zijlstra wrote:
> > > On Mon, 2010-05-10 at 18:17 +0800, Lin Ming wrote:
> > > > On Mon, 2010-05-10 at 17:40 +0800, Peter Zijlstra wrote:
> > > > > On Mon, 2010-05-10 at 17:26 +0800, Lin Ming wrote:
> > > > > > +static struct pmu *perf_event_lookup_pmu(struct perf_event *event)
> > > > > > +{
> > > > > > +       struct pmu *pmu;
> > > > > > +       int pmu_id = event->attr.pmu_id;
> > > > > > +
> > > > > > +       list_for_each_entry(pmu, &pmus, entry) {
> > > > > > +               if (pmu->id == pmu_id)
> > > > > > +                       return pmu;
> > > > > > +       }
> > > > > > +
> > > > > > +       return NULL;
> > > > > > +}
> > > > > 
> > > > > > +void perf_event_register_pmu(struct pmu *pmu)
> > > > > > +{
> > > > > > +       pmu->id = pmu_id_curr++;
> > > > > > +       list_add_tail(&pmu->entry, &pmus);
> > > > > > +} 
> > > > > 
> > > > > That will be wanting some sort of synchronization
> > > > 
> > > > Will add a mutex to protect the list of pmus.
> > > 
> > > I'm thinking RCU might be better suited, a mutex for lookup doesn't
> > > sound ideal.
> > 
> > 
> > Is it really needed? I expect this function to be called on boot
> > only.
> > 
> > In fact I would even suggest to tag it as __init.
> 
> Loadable modules as well as PCI-Hotplug need supporting.


Which module do you have in mind that could register a pmu?
And I don't understand the problem with pci-hotplug.

Thanks.