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Date: Sat, 16 May 2020 01:45:48 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: LKML <linux-kernel@...r.kernel.org>
Cc: x86@...nel.org, "Paul E. McKenney" <paulmck@...nel.org>,
Andy Lutomirski <luto@...nel.org>,
Alexandre Chartre <alexandre.chartre@...cle.com>,
Frederic Weisbecker <frederic@...nel.org>,
Paolo Bonzini <pbonzini@...hat.com>,
Sean Christopherson <sean.j.christopherson@...el.com>,
Masami Hiramatsu <mhiramat@...nel.org>,
Petr Mladek <pmladek@...e.com>,
Steven Rostedt <rostedt@...dmis.org>,
Joel Fernandes <joel@...lfernandes.org>,
Boris Ostrovsky <boris.ostrovsky@...cle.com>,
Juergen Gross <jgross@...e.com>,
Brian Gerst <brgerst@...il.com>,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
Josh Poimboeuf <jpoimboe@...hat.com>,
Will Deacon <will@...nel.org>,
Tom Lendacky <thomas.lendacky@....com>,
Wei Liu <wei.liu@...nel.org>,
Michael Kelley <mikelley@...rosoft.com>,
Jason Chen CJ <jason.cj.chen@...el.com>,
Zhao Yakui <yakui.zhao@...el.com>,
"Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: [patch V6 01/37] tracing/hwlat: Use ktime_get_mono_fast_ns()
Timestamping in the hardware latency detector uses sched_clock() underneath
and depends on CONFIG_GENERIC_SCHED_CLOCK=n because sched clocks from that
subsystem are not NMI safe.
ktime_get_mono_fast_ns() is NMI safe and available on all architectures.
Replace the time getter, get rid of the CONFIG_GENERIC_SCHED_CLOCK=n
dependency and cleanup the horrible macro maze which encapsulates u64 math
in u64 macros.
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
kernel/trace/trace_hwlat.c | 59 +++++++++++++++++++--------------------------
1 file changed, 25 insertions(+), 34 deletions(-)
--- a/kernel/trace/trace_hwlat.c
+++ b/kernel/trace/trace_hwlat.c
@@ -131,29 +131,19 @@ static void trace_hwlat_sample(struct hw
trace_buffer_unlock_commit_nostack(buffer, event);
}
-/* Macros to encapsulate the time capturing infrastructure */
-#define time_type u64
-#define time_get() trace_clock_local()
-#define time_to_us(x) div_u64(x, 1000)
-#define time_sub(a, b) ((a) - (b))
-#define init_time(a, b) (a = b)
-#define time_u64(a) a
-
+/*
+ * Timestamping uses ktime_get_mono_fast(), the NMI safe access to
+ * CLOCK_MONOTONIC.
+ */
void trace_hwlat_callback(bool enter)
{
if (smp_processor_id() != nmi_cpu)
return;
- /*
- * Currently trace_clock_local() calls sched_clock() and the
- * generic version is not NMI safe.
- */
- if (!IS_ENABLED(CONFIG_GENERIC_SCHED_CLOCK)) {
- if (enter)
- nmi_ts_start = time_get();
- else
- nmi_total_ts += time_get() - nmi_ts_start;
- }
+ if (enter)
+ nmi_ts_start = ktime_get_mono_fast_ns();
+ else
+ nmi_total_ts += ktime_get_mono_fast_ns() - nmi_ts_start;
if (enter)
nmi_count++;
@@ -165,20 +155,22 @@ void trace_hwlat_callback(bool enter)
* Used to repeatedly capture the CPU TSC (or similar), looking for potential
* hardware-induced latency. Called with interrupts disabled and with
* hwlat_data.lock held.
+ *
+ * Use ktime_get_mono_fast() here as well because it does not wait on the
+ * timekeeping seqcount like ktime_get_mono().
*/
static int get_sample(void)
{
struct trace_array *tr = hwlat_trace;
struct hwlat_sample s;
- time_type start, t1, t2, last_t2;
+ u64 start, t1, t2, last_t2, thresh;
s64 diff, outer_diff, total, last_total = 0;
u64 sample = 0;
- u64 thresh = tracing_thresh;
u64 outer_sample = 0;
int ret = -1;
unsigned int count = 0;
- do_div(thresh, NSEC_PER_USEC); /* modifies interval value */
+ thresh = div_u64(tracing_thresh, NSEC_PER_USEC);
nmi_cpu = smp_processor_id();
nmi_total_ts = 0;
@@ -188,18 +180,20 @@ static int get_sample(void)
trace_hwlat_callback_enabled = true;
- init_time(last_t2, 0);
- start = time_get(); /* start timestamp */
+ /* start timestamp */
+ start = ktime_get_mono_fast_ns();
outer_diff = 0;
+ last_t2 = 0;
do {
- t1 = time_get(); /* we'll look for a discontinuity */
- t2 = time_get();
+ /* we'll look for a discontinuity */
+ t1 = ktime_get_mono_fast_ns();
+ t2 = ktime_get_mono_fast_ns();
- if (time_u64(last_t2)) {
+ if (last_t2) {
/* Check the delta from outer loop (t2 to next t1) */
- outer_diff = time_to_us(time_sub(t1, last_t2));
+ outer_diff = div_u64(t1 - last_t2, NSEC_PER_USEC);
/* This shouldn't happen */
if (outer_diff < 0) {
pr_err(BANNER "time running backwards\n");
@@ -210,7 +204,8 @@ static int get_sample(void)
}
last_t2 = t2;
- total = time_to_us(time_sub(t2, start)); /* sample width */
+ /* sample width */
+ total = div_u64(t2 - start, NSEC_PER_USEC);
/* Check for possible overflows */
if (total < last_total) {
@@ -220,7 +215,7 @@ static int get_sample(void)
last_total = total;
/* This checks the inner loop (t1 to t2) */
- diff = time_to_us(time_sub(t2, t1)); /* current diff */
+ diff = div_u64(t2 - t1, NSEC_PER_USEC);
if (diff > thresh || outer_diff > thresh) {
if (!count)
@@ -251,15 +246,11 @@ static int get_sample(void)
ret = 1;
- /* We read in microseconds */
- if (nmi_total_ts)
- do_div(nmi_total_ts, NSEC_PER_USEC);
-
hwlat_data.count++;
s.seqnum = hwlat_data.count;
s.duration = sample;
s.outer_duration = outer_sample;
- s.nmi_total_ts = nmi_total_ts;
+ s.nmi_total_ts = div_u64(nmi_total_ts, NSEC_PER_USEC);
s.nmi_count = nmi_count;
s.count = count;
trace_hwlat_sample(&s);
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