linux-kernel - [PATCH v1 6/7] perf/x86/intel/pt: Kill pt_is

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Date:	Fri, 22 May 2015 18:30:25 +0300
From:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...hat.com>
Cc:	linux-kernel@...r.kernel.org, Paul Mackerras <paulus@...ba.org>,
	adrian.hunter@...el.com, x86@...nel.org, hpa@...or.com,
	acme@...radead.org,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Subject: [PATCH v1 6/7] perf/x86/intel/pt: Kill pt_is_running()

Initially, we were trying to guard against scenarios where somebody
attaches to the system with a hardware debugger while PT is enabled
from software and pt_is_running() tries to make sure we handle this
better, but the truth is, there is still a race window no matter what
and people with hardware debuggers should really know what they are
doing anyway. In other words, there is no point in keeping this one
around, and it's one rdmsr fewer in the fast path.

One case when PT is enabled by the bios at the boot time is handled
in driver initialization path and doesn't use pt_is_running().

This patch gets rid of it.

Signed-off-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
---
 arch/x86/kernel/cpu/perf_event_intel_pt.c | 11 +----------
 1 file changed, 1 insertion(+), 10 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_event_intel_pt.c b/arch/x86/kernel/cpu/perf_event_intel_pt.c
index 40ba5e4312..a2d407172d 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_pt.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_pt.c
@@ -187,15 +187,6 @@ static bool pt_event_valid(struct perf_event *event)
  * These all are cpu affine and operate on a local PT
  */
 
-static bool pt_is_running(void)
-{
-	u64 ctl;
-
-	rdmsrl(MSR_IA32_RTIT_CTL, ctl);
-
-	return !!(ctl & RTIT_CTL_TRACEEN);
-}
-
 static void pt_config(struct perf_event *event)
 {
 	u64 reg;
@@ -933,7 +924,7 @@ static void pt_event_start(struct perf_event *event, int mode)
 	struct pt *pt = this_cpu_ptr(&pt_ctx);
 	struct pt_buffer *buf = perf_get_aux(&pt->handle);
 
-	if (pt_is_running() || !buf || pt_buffer_is_full(buf, pt)) {
+	if (!buf || pt_buffer_is_full(buf, pt)) {
 		event->hw.state = PERF_HES_STOPPED;
 		return;
 	}
-- 
2.1.4

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