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 instructions fewer in the fast path.

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

This patch gets rid of it.

Signed-off-by: Alexander Shishkin <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Link: http://lkml.kernel.org/r/1429622177-22843-6-git-send-email-alexander.shishkin@linux.intel.com
Signed-off-by: Ingo Molnar <[email protected]>

diff --git a/arch/x86/kernel/cpu/perf_event_intel_pt.c b/arch/x86/kernel/cpu/perf_event_intel_pt.c
index 40ba5e4312d40999bc381721969621d33bc010a6..a2d407172d61a0f0b2aa75263ce835f7dc8c0e84 100644 (file)
--- 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;
        }