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>

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 9edb628..5434c16 100644 (file)
--- 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 48d5eb2..d382fd1 100644 (file)
--- 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 ab16eca..0890082 100644 (file)
--- 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];