From: Matt Fleming <matt@console-pimps.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>, Jiri Olsa <jolsa@redhat.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Andi Kleen <andi@firstfloor.org>,
Thomas Gleixner <tglx@linutronix.de>,
linux-kernel@vger.kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
Kanaka Juvva <kanaka.d.juvva@intel.com>,
Matt Fleming <matt.fleming@intel.com>
Subject: Re: [PATCH v4 10/11] perf/x86/intel: Perform rotation on Intel CQM RMIDs
Date: Fri, 9 Jan 2015 12:22:39 +0000 [thread overview]
Message-ID: <20150109122239.GC495@console-pimps.org> (raw)
In-Reply-To: <20150106173641.GI3337@twins.programming.kicks-ass.net>
On Tue, 06 Jan, at 06:36:41PM, Peter Zijlstra wrote:
> On Fri, Nov 14, 2014 at 09:15:11PM +0000, Matt Fleming wrote:
> > @@ -417,17 +857,38 @@ static u64 intel_cqm_event_count(struct perf_event *event)
> > if (!cqm_group_leader(event))
> > return 0;
> >
> > - on_each_cpu_mask(&cqm_cpumask, __intel_cqm_event_count, &rr, 1);
> > + /*
> > + * Notice that we don't perform the reading of an RMID
> > + * atomically, because we can't hold a spin lock across the
> > + * IPIs.
> > + *
> > + * Speculatively perform the read, since @event might be
> > + * assigned a different (possibly invalid) RMID while we're
> > + * busying performing the IPI calls. It's therefore necessary to
> > + * check @event's RMID afterwards, and if it has changed,
> > + * discard the result of the read.
> > + */
> > + raw_spin_lock_irqsave(&cache_lock, flags);
> > + rr.rmid = event->hw.cqm_rmid;
> > + raw_spin_unlock_irqrestore(&cache_lock, flags);
>
> You don't actually have to hold the lock here, only ACCESS_ONCE() or
> whatever newfangled thing replaced that.
Remind me again, are accesses to 'int' guaranteed to be atomic? There's
no way to read a partial value?
--
Matt Fleming, Intel Open Source Technology Center
next prev parent reply other threads:[~2015-01-09 12:29 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-11-14 21:15 [PATCH v4 00/11] perf: Intel Cache QoS Monitoring support Matt Fleming
2014-11-14 21:15 ` [PATCH 01/11] perf tools: Parse event per-package info files Matt Fleming
2014-11-14 21:15 ` [PATCH 02/11] perf tools: Implement snapshot event file logic Matt Fleming
2014-11-14 21:15 ` [PATCH 03/11] perf: Make perf_cgroup_from_task() global Matt Fleming
2014-11-14 21:15 ` [PATCH 04/11] perf: Add ->count() function to read per-package counters Matt Fleming
2014-11-14 21:15 ` [PATCH 05/11] perf: Move cgroup init before PMU ->event_init() Matt Fleming
2014-11-14 21:15 ` [PATCH 06/11] x86: Add support for Intel Cache QoS Monitoring (CQM) detection Matt Fleming
2014-11-14 21:15 ` [PATCH 07/11] perf/x86/intel: Add Intel Cache QoS Monitoring support Matt Fleming
2014-11-14 21:15 ` [PATCH 08/11] perf/x86/intel: Implement LRU monitoring ID allocation for CQM Matt Fleming
2014-11-14 21:15 ` [PATCH v4 09/11] perf/x86/intel: Support task events with Intel CQM Matt Fleming
2014-11-14 21:15 ` [PATCH v4 10/11] perf/x86/intel: Perform rotation on Intel CQM RMIDs Matt Fleming
2015-01-06 16:13 ` Peter Zijlstra
2015-01-06 17:17 ` Peter Zijlstra
2015-01-09 12:14 ` Matt Fleming
2015-01-09 13:02 ` Peter Zijlstra
2015-01-09 15:24 ` Matt Fleming
2015-01-09 15:58 ` Peter Zijlstra
2015-01-15 15:31 ` Matt Fleming
2015-01-15 19:37 ` Matt Fleming
2015-01-06 17:36 ` Peter Zijlstra
2015-01-09 12:22 ` Matt Fleming [this message]
2015-01-09 12:59 ` Peter Zijlstra
2015-01-07 12:16 ` Peter Zijlstra
2015-01-09 12:55 ` Matt Fleming
2015-01-09 12:58 ` Peter Zijlstra
2015-01-11 10:45 ` Matt Fleming
2014-11-14 21:15 ` [PATCH 11/11] perf/x86/intel: Enable conflicting event scheduling for CQM Matt Fleming
2015-01-08 11:49 ` Peter Zijlstra
2015-01-09 12:56 ` Matt Fleming
2015-01-08 11:51 ` Peter Zijlstra
2015-01-09 14:27 ` Matt Fleming
2014-11-25 14:55 ` [PATCH v4 00/11] perf: Intel Cache QoS Monitoring support Matt Fleming
2014-12-18 7:59 ` Matt Fleming
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