linux-kernel - [PATCH 2/2] perf, x86: Enable PDIR precise instruction profiling on IvyBridge

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <1339615201-7456-2-git-send-email-andi@firstfloor.org>
Date:	Wed, 13 Jun 2012 12:20:01 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	mingo@...e.hu
Cc:	linux-kernel@...r.kernel.org, a.p.zijlstra@...llo.nl,
	Andi Kleen <ak@...ux.intel.com>
Subject: [PATCH 2/2] perf, x86: Enable PDIR precise instruction profiling on IvyBridge

From: Andi Kleen <ak@...ux.intel.com>

Even with precise profiling Intel CPUs have a "skid". The sample
triggers a few cycles later than the instruction, so in some
cases there can be systematic errors where expensive instructions never
show up in the profile log.

Sandy Bridge added a new PDIR instruction retired event that randomizes
the sampling slightly. This corrects for systematic errors, so that
you should in most cases see the correct instruction getting profile hits.

Unfortunately the SandyBridge version could only work with a otherwise
quiescent CPU and was difficult to use. But now on IvyBridge this
restriction is gone and can be more widely used.

This only works for retired instructions.

I enabled it -- somewhat arbitarily -- for two 'p's or more.

To use it

perf record -e instructions:pp ...

This provides a more precise alternative to the usual cycles:pp,
however it will not account for expensive instructions.

Signed-off-by: Andi Kleen <ak@...ux.intel.com>
---
 arch/x86/kernel/cpu/perf_event_intel.c |   23 +++++++++++++++++++++++
 1 files changed, 23 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c
index abb29c2..886d124 100644
--- a/arch/x86/kernel/cpu/perf_event_intel.c
+++ b/arch/x86/kernel/cpu/perf_event_intel.c
@@ -1425,6 +1425,28 @@ static int intel_pmu_hw_config(struct perf_event *event)
 	return 0;
 }
 
+static int pdir_hw_config(struct perf_event *event)
+{
+	int err = intel_pmu_hw_config(event);
+
+	if (err)
+		return err;
+
+	/* 
+	 * Use the PDIR instruction retired counter for two 'p's.
+	 * This will randomize samples slightly and avoid some systematic 
+	 * measurement errors.
+	 * Only works for retired cycles.
+	 */
+	if (event->attr.precise_ip >= 2 &&
+	    (event->hw.config & X86_RAW_EVENT_MASK) == 0xc0) {
+		u64 pdir_event = X86_CONFIG(.event=0xc0, .umask=1);
+		event->hw.config = pdir_event | (event->hw.config & ~X86_RAW_EVENT_MASK);
+	}
+
+	return 0;
+}
+
 struct perf_guest_switch_msr *perf_guest_get_msrs(int *nr)
 {
 	if (x86_pmu.guest_get_msrs)
@@ -1943,6 +1965,7 @@ __init int intel_pmu_init(void)
 		x86_pmu.event_constraints = intel_snb_event_constraints;
 		x86_pmu.pebs_constraints = intel_snb_pebs_event_constraints;
 		x86_pmu.extra_regs = intel_snb_extra_regs;
+		x86_pmu.hw_config = pdir_hw_config;
 		/* all extra regs are per-cpu when HT is on */
 		x86_pmu.er_flags |= ERF_HAS_RSP_1;
 		x86_pmu.er_flags |= ERF_NO_HT_SHARING;
-- 
1.7.7.6

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/