tracing: Add tracefs file buffer_percentage

Add a "buffer_percentage" file, that allows users to specify how much of the
buffer (percentage of pages) need to be filled before waking up a task
blocked on a per cpu trace_pipe_raw file.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

3 files changed, 77 insertions, 17 deletions

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 9edb628603ab..5434c16f2192 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -489,6 +489,7 @@ struct ring_buffer_per_cpu {
         local_t                         commits;
         local_t                         pages_touched;
         local_t                         pages_read;
+        long                            last_pages_touch;
         size_t                          shortest_full;
         unsigned long                   read;
         unsigned long                   read_bytes;
@@ -2632,7 +2633,9 @@ static void rb_commit(struct ring_buffer_per_cpu *cpu_buffer,
 static __always_inline void
 rb_wakeups(struct ring_buffer *buffer, struct ring_buffer_per_cpu *cpu_buffer)
 {
-        bool pagebusy;
+        size_t nr_pages;
+        size_t dirty;
+        size_t full;
 
         if (buffer->irq_work.waiters_pending) {
                 buffer->irq_work.waiters_pending = false;
@@ -2646,24 +2649,27 @@ rb_wakeups(struct ring_buffer *buffer, struct ring_buffer_per_cpu *cpu_buffer)
                 irq_work_queue(&cpu_buffer->irq_work.work);
         }
 
-        pagebusy = cpu_buffer->reader_page == cpu_buffer->commit_page;
+        if (cpu_buffer->last_pages_touch == local_read(&cpu_buffer->pages_touched))
+                return;
 
-        if (!pagebusy && cpu_buffer->irq_work.full_waiters_pending) {
-                size_t nr_pages;
-                size_t dirty;
-                size_t full;
+        if (cpu_buffer->reader_page == cpu_buffer->commit_page)
+                return;
 
-                full = cpu_buffer->shortest_full;
-                nr_pages = cpu_buffer->nr_pages;
-                dirty = ring_buffer_nr_dirty_pages(buffer, cpu_buffer->cpu);
-                if (full && nr_pages && (dirty * 100) <= full * nr_pages)
-                        return;
+        if (!cpu_buffer->irq_work.full_waiters_pending)
+                return;
 
-                cpu_buffer->irq_work.wakeup_full = true;
-                cpu_buffer->irq_work.full_waiters_pending = false;
-                /* irq_work_queue() supplies it's own memory barriers */
-                irq_work_queue(&cpu_buffer->irq_work.work);
-        }
+        cpu_buffer->last_pages_touch = local_read(&cpu_buffer->pages_touched);
+
+        full = cpu_buffer->shortest_full;
+        nr_pages = cpu_buffer->nr_pages;
+        dirty = ring_buffer_nr_dirty_pages(buffer, cpu_buffer->cpu);
+        if (full && nr_pages && (dirty * 100) <= full * nr_pages)
+                return;
+
+        cpu_buffer->irq_work.wakeup_full = true;
+        cpu_buffer->irq_work.full_waiters_pending = false;
+        /* irq_work_queue() supplies it's own memory barriers */
+        irq_work_queue(&cpu_buffer->irq_work.work);
 }
 
 /*
@@ -4394,6 +4400,7 @@ rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
         local_set(&cpu_buffer->commits, 0);
         local_set(&cpu_buffer->pages_touched, 0);
         local_set(&cpu_buffer->pages_read, 0);
+        cpu_buffer->last_pages_touch = 0;
         cpu_buffer->shortest_full = 0;
         cpu_buffer->read = 0;
         cpu_buffer->read_bytes = 0;
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 48d5eb22ff33..d382fd1aa4a6 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -6948,7 +6948,7 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos,
                 if ((file->f_flags & O_NONBLOCK) || (flags & SPLICE_F_NONBLOCK))
                         goto out;
 
-                ret = wait_on_pipe(iter, 1);
+                ret = wait_on_pipe(iter, iter->tr->buffer_percent);
                 if (ret)
                         goto out;
 
@@ -7662,6 +7662,53 @@ static const struct file_operations rb_simple_fops = {
         .llseek         = default_llseek,
 };
 
+static ssize_t
+buffer_percent_read(struct file *filp, char __user *ubuf,
+                    size_t cnt, loff_t *ppos)
+{
+        struct trace_array *tr = filp->private_data;
+        char buf[64];
+        int r;
+
+        r = tr->buffer_percent;
+        r = sprintf(buf, "%d\n", r);
+
+        return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
+}
+
+static ssize_t
+buffer_percent_write(struct file *filp, const char __user *ubuf,
+                     size_t cnt, loff_t *ppos)
+{
+        struct trace_array *tr = filp->private_data;
+        unsigned long val;
+        int ret;
+
+        ret = kstrtoul_from_user(ubuf, cnt, 10, &val);
+        if (ret)
+                return ret;
+
+        if (val > 100)
+                return -EINVAL;
+
+        if (!val)
+                val = 1;
+
+        tr->buffer_percent = val;
+
+        (*ppos)++;
+
+        return cnt;
+}
+
+static const struct file_operations buffer_percent_fops = {
+        .open           = tracing_open_generic_tr,
+        .read           = buffer_percent_read,
+        .write          = buffer_percent_write,
+        .release        = tracing_release_generic_tr,
+        .llseek         = default_llseek,
+};
+
 struct dentry *trace_instance_dir;
 
 static void
@@ -7970,6 +8017,11 @@ init_tracer_tracefs(struct trace_array *tr, struct dentry *d_tracer)
         trace_create_file("timestamp_mode", 0444, d_tracer, tr,
                           &trace_time_stamp_mode_fops);
 
+        tr->buffer_percent = 1;
+
+        trace_create_file("buffer_percent", 0444, d_tracer,
+                        tr, &buffer_percent_fops);
+
         create_trace_options_dir(tr);
 
 #if defined(CONFIG_TRACER_MAX_TRACE) || defined(CONFIG_HWLAT_TRACER)
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index ab16eca76e59..08900828d282 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -247,6 +247,7 @@ struct trace_array {
         int                     clock_id;
         int                     nr_topts;
         bool                    clear_trace;
+        int                     buffer_percent;
         struct tracer           *current_trace;
         unsigned int            trace_flags;
         unsigned char           trace_flags_index[TRACE_FLAGS_MAX_SIZE];