trace/hwlat: Switch disable_migrate to mode none

When in the round-robin mode, if the tracer detects a change in the
hwlatd thread affinity by an external tool, e.g., taskset, the
round-robin logic is disabled. The disable_migrate variable currently
tracks this.

With the addition of the "mode" config and the mode "none," the
disable_migrate logic is equivalent to switch to the "none" mode.

Hence, instead of using a hidden variable to track this behavior,
switch the mode to none, informing the user about this change.

Link: https://lkml.kernel.org/r/a679af672458d6b1f62252605905c5214030f247.1624372313.git.bristot@redhat.com
Cc: Phil Auld <pauld@redhat.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Kate Carcia <kcarcia@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Alexandre Chartre <alexandre.chartre@oracle.com>
Cc: Clark Willaims <williams@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace_hwlat.c b/kernel/trace/trace_hwlat.c
index 43a436d85a01787d91981b805b94c0d44176fa45..bae74b95cf5526950664f4721ff98bbf3f7a0c2a 100644 (file)
--- a/kernel/trace/trace_hwlat.c
+++ b/kernel/trace/trace_hwlat.c
@@ -286,7 +286,6 @@ out:
 }
 
 static struct cpumask save_cpumask;
-static bool disable_migrate;
 
 static void move_to_next_cpu(void)
 {
@@ -294,15 +293,13 @@ static void move_to_next_cpu(void)
        struct trace_array *tr = hwlat_trace;
        int next_cpu;
 
-       if (disable_migrate)
-               return;
        /*
         * If for some reason the user modifies the CPU affinity
         * of this thread, then stop migrating for the duration
         * of the current test.
         */
        if (!cpumask_equal(current_mask, current->cpus_ptr))
-               goto disable;
+               goto change_mode;
 
        get_online_cpus();
        cpumask_and(current_mask, cpu_online_mask, tr->tracing_cpumask);
@@ -313,7 +310,7 @@ static void move_to_next_cpu(void)
                next_cpu = cpumask_first(current_mask);
 
        if (next_cpu >= nr_cpu_ids) /* Shouldn't happen! */
-               goto disable;
+               goto change_mode;
 
        cpumask_clear(current_mask);
        cpumask_set_cpu(next_cpu, current_mask);
@@ -321,8 +318,9 @@ static void move_to_next_cpu(void)
        sched_setaffinity(0, current_mask);
        return;
 
- disable:
-       disable_migrate = true;
+ change_mode:
+       hwlat_data.thread_mode = MODE_NONE;
+       pr_info(BANNER "cpumask changed while in round-robin mode, switching to mode none\n");
 }
 
 /*
@@ -744,7 +742,6 @@ static int hwlat_tracer_init(struct trace_array *tr)
 
        hwlat_trace = tr;
 
-       disable_migrate = false;
        hwlat_data.count = 0;
        tr->max_latency = 0;
        save_tracing_thresh = tracing_thresh;