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Message-ID: <20150627083921.GA13074@gmail.com>
Date: Sat, 27 Jun 2015 10:39:21 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Prarit Bhargava <prarit@...hat.com>
Cc: linux-kernel@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
Len Brown <len.brown@...el.com>,
Dasaratharaman Chandramouli
<dasaratharaman.chandramouli@...el.com>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Borislav Petkov <bp@...en8.de>,
Andy Lutomirski <luto@...nel.org>,
Denys Vlasenko <dvlasenk@...hat.com>,
Brian Gerst <brgerst@...il.com>,
Arnaldo Carvalho de Melo <acme@...radead.org>
Subject: Re: [PATCH] x86, msr: Allow read access to /dev/cpu/X/msr
* Ingo Molnar <mingo@...nel.org> wrote:
> So what's wrong with exposing them as a simplified PMU driver?
>
> That way we only expose the ones we want to - plus tooling can use all the rich
> perf features that can be used around this. (sampling, counting, call chains,
> etc.)
See below code from Andy that exposes a single MSR via perf. At the core of the
PMU driver is a single rdmsrl():
+static void aperfmperf_event_start(struct perf_event *event, int flags)
+{
+ u64 now;
+
+ rdmsrl(event->hw.event_base, now);
+ local64_set(&event->hw.prev_count, now);
+}
Now I think what we really want is to expose not a single MSR but multiple MSRs in
a single driver, i.e. don't have one PMU driver per MSR, but have a driver that
allows the exposure of select MSRs as counters.
There should also be a maker/family/model filter mechanism, so that certain MSRs
are only exposed on models that are known to support them, etc.
Thanks,
Ingo
----- Forwarded message from Andy Lutomirski <luto@...nel.org> -----
Date: Tue, 28 Apr 2015 14:25:37 -0700
From: Andy Lutomirski <luto@...nel.org>
To: Len Brown <len.brown@...el.com>, Peter Zijlstra <peterz@...radead.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc: Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...hat.com>, Arnaldo Carvalho de Melo <acme@...nel.org>, Andy Lutomirski <luto@...nel.org>
Subject: [RFC] x86, perf: Add an aperfmperf driver
Signed-off-by: Andy Lutomirski <luto@...nel.org>
---
This driver seems a little bit silly, but I can imagine it being useful. For
example, I think that turbostat could do some of its work without being
root if we had a driver like this.
Thoughts? Would it make sense at all? Did I wire it up right? This is
the only PMU driver I've ever written, and it could have any number of
issues.
arch/x86/kernel/cpu/Makefile | 2 +
arch/x86/kernel/cpu/perf_event_aperfmperf.c | 119 ++++++++++++++++++++++++++++
2 files changed, 121 insertions(+)
create mode 100644 arch/x86/kernel/cpu/perf_event_aperfmperf.c
diff --git a/arch/x86/kernel/cpu/Makefile b/arch/x86/kernel/cpu/Makefile
index 80091ae54c2b..fadc822efc90 100644
--- a/arch/x86/kernel/cpu/Makefile
+++ b/arch/x86/kernel/cpu/Makefile
@@ -45,6 +45,8 @@ obj-$(CONFIG_PERF_EVENTS_INTEL_UNCORE) += perf_event_intel_uncore.o \
perf_event_intel_uncore_snb.o \
perf_event_intel_uncore_snbep.o \
perf_event_intel_uncore_nhmex.o
+obj-$(CONFIG_CPU_SUP_INTEL) += perf_event_aperf_mperf.o
+obj-$(CONFIG_CPU_SUP_AMD) += perf_event_aperf_mperf.o
endif
diff --git a/arch/x86/kernel/cpu/perf_event_aperfmperf.c b/arch/x86/kernel/cpu/perf_event_aperfmperf.c
new file mode 100644
index 000000000000..6e6d113bd9ce
--- /dev/null
+++ b/arch/x86/kernel/cpu/perf_event_aperfmperf.c
@@ -0,0 +1,119 @@
+#include <linux/perf_event.h>
+
+#define APERFMPERF_EVENT_APERF 0
+#define APERFMPERF_EVENT_MPERF 1
+
+PMU_EVENT_ATTR_STRING(aperf, evattr_aperf, "event=0x00");
+PMU_EVENT_ATTR_STRING(mperf, evattr_mperf, "event=0x01");
+static struct attribute *events_attrs[] = {
+ &evattr_aperf.attr.attr,
+ &evattr_mperf.attr.attr,
+ NULL,
+};
+static struct attribute_group events_attr_group = {
+ .name = "events",
+ .attrs = events_attrs,
+};
+
+PMU_FORMAT_ATTR(event, "config:0-63");
+static struct attribute *format_attrs[] = {
+ &format_attr_event.attr,
+ NULL,
+};
+static struct attribute_group format_attr_group = {
+ .name = "format",
+ .attrs = format_attrs,
+};
+
+static const struct attribute_group *attr_groups[] = {
+ &events_attr_group,
+ &format_attr_group,
+ NULL,
+};
+
+static int aperfmperf_event_init(struct perf_event *event)
+{
+ if (event->attr.type != event->pmu->type)
+ return -ENOENT;
+
+ if (event->attr.config != APERFMPERF_EVENT_APERF &&
+ event->attr.config != APERFMPERF_EVENT_MPERF)
+ return -ENOENT;
+
+ if (event->attr.config1 != 0)
+ return -ENOENT;
+
+ /* no sampling */
+ if (event->hw.sample_period)
+ return -EINVAL;
+
+ /* unsupported modes and filters */
+ if (event->attr.exclude_user ||
+ event->attr.exclude_kernel ||
+ event->attr.exclude_hv ||
+ event->attr.exclude_idle ||
+ event->attr.exclude_host ||
+ event->attr.exclude_guest ||
+ event->attr.freq ||
+ event->attr.sample_period) /* no sampling */
+ return -EINVAL;
+
+ event->hw.idx = -1;
+ event->hw.event_base = (event->attr.config == APERFMPERF_EVENT_APERF ?
+ MSR_IA32_APERF : MSR_IA32_MPERF);
+
+ return 0;
+}
+
+static void aperfmperf_event_update(struct perf_event *event)
+{
+ u64 prev;
+ u64 now;
+
+ rdmsrl(event->hw.event_base, now);
+ prev = local64_xchg(&event->hw.prev_count, now);
+ local64_add(now - prev, &event->count);
+}
+
+static void aperfmperf_event_start(struct perf_event *event, int flags)
+{
+ u64 now;
+
+ rdmsrl(event->hw.event_base, now);
+ local64_set(&event->hw.prev_count, now);
+}
+
+static void aperfmperf_event_stop_or_del(struct perf_event *event, int flags)
+{
+ aperfmperf_event_update(event);
+}
+
+static int aperfmperf_event_add(struct perf_event *event, int flags)
+{
+ if (flags & PERF_EF_START)
+ aperfmperf_event_start(event, flags);
+
+ return 0;
+}
+
+static struct pmu pmu_aperfmperf = {
+ .task_ctx_nr = perf_invalid_context,
+ .attr_groups = attr_groups,
+ .event_init = aperfmperf_event_init,
+ .add = aperfmperf_event_add,
+ .del = aperfmperf_event_stop_or_del,
+ .start = aperfmperf_event_start,
+ .stop = aperfmperf_event_stop_or_del,
+ .read = aperfmperf_event_update,
+};
+
+static int __init aperfmperf_init(void)
+{
+ if (!boot_cpu_has(X86_FEATURE_APERFMPERF))
+ return -ENODEV;
+
+ perf_pmu_register(&pmu_aperfmperf, "aperfmperf", -1);
+
+ return 0;
+}
+device_initcall(aperfmperf_init);
--
2.3.0
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