ring-buffer: Add interface for configuring trace sub buffer size

The trace ring buffer sub page size can be configured, per trace
instance. A new ftrace file "buffer_subbuf_order" is added to get and
set the size of the ring buffer sub page for current trace instance.
The size must be an order of system page size, that's why the new
interface works with system page order, instead of absolute page size:
0 means the ring buffer sub page is equal to 1 system page and so
forth:
0 - 1 system page
1 - 2 system pages
2 - 4 system pages
...
The ring buffer sub page size is limited between 1 and 128 system
pages. The default value is 1 system page.
New ring buffer APIs are introduced:
 ring_buffer_subbuf_order_set()
 ring_buffer_subbuf_order_get()
 ring_buffer_subbuf_size_get()

Link: https://lore.kernel.org/linux-trace-devel/20211213094825.61876-4-tz.stoyanov@gmail.com
Link: https://lore.kernel.org/linux-trace-kernel/20231219185628.298324722@goodmis.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Vincent Donnefort <vdonnefort@google.com>
Cc: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
index ce46218ce46df4be95f56ea15b7acf7780de3638..12573306b8892c06af2a11232a3f52cb01d1ddcd 100644 (file)
--- a/include/linux/ring_buffer.h
+++ b/include/linux/ring_buffer.h
@@ -202,6 +202,10 @@ struct trace_seq;
 int ring_buffer_print_entry_header(struct trace_seq *s);
 int ring_buffer_print_page_header(struct trace_buffer *buffer, struct trace_seq *s);
 
+int ring_buffer_subbuf_order_get(struct trace_buffer *buffer);
+int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order);
+int ring_buffer_subbuf_size_get(struct trace_buffer *buffer);
+
 enum ring_buffer_flags {
        RB_FL_OVERWRITE         = 1 << 0,
 };

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index d9f6565024004667970b0e2c96f56f61189fae5a..20fc0121735d3aacc919eee7fce57c8d3ff3b86d 100644 (file)
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -507,6 +507,7 @@ struct trace_buffer {
        bool                            time_stamp_abs;
 
        unsigned int                    subbuf_size;
+       unsigned int                    subbuf_order;
        unsigned int                    max_data_size;
 };
 
@@ -5761,6 +5762,78 @@ int ring_buffer_read_page(struct trace_buffer *buffer,
 }
 EXPORT_SYMBOL_GPL(ring_buffer_read_page);
 
+/**
+ * ring_buffer_subbuf_size_get - get size of the sub buffer.
+ * @buffer: the buffer to get the sub buffer size from
+ *
+ * Returns size of the sub buffer, in bytes.
+ */
+int ring_buffer_subbuf_size_get(struct trace_buffer *buffer)
+{
+       return buffer->subbuf_size + BUF_PAGE_HDR_SIZE;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_subbuf_size_get);
+
+/**
+ * ring_buffer_subbuf_order_get - get order of system sub pages in one buffer page.
+ * @buffer: The ring_buffer to get the system sub page order from
+ *
+ * By default, one ring buffer sub page equals to one system page. This parameter
+ * is configurable, per ring buffer. The size of the ring buffer sub page can be
+ * extended, but must be an order of system page size.
+ *
+ * Returns the order of buffer sub page size, in system pages:
+ * 0 means the sub buffer size is 1 system page and so forth.
+ * In case of an error < 0 is returned.
+ */
+int ring_buffer_subbuf_order_get(struct trace_buffer *buffer)
+{
+       if (!buffer)
+               return -EINVAL;
+
+       return buffer->subbuf_order;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_subbuf_order_get);
+
+/**
+ * ring_buffer_subbuf_order_set - set the size of ring buffer sub page.
+ * @buffer: The ring_buffer to set the new page size.
+ * @order: Order of the system pages in one sub buffer page
+ *
+ * By default, one ring buffer pages equals to one system page. This API can be
+ * used to set new size of the ring buffer page. The size must be order of
+ * system page size, that's why the input parameter @order is the order of
+ * system pages that are allocated for one ring buffer page:
+ *  0 - 1 system page
+ *  1 - 2 system pages
+ *  3 - 4 system pages
+ *  ...
+ *
+ * Returns 0 on success or < 0 in case of an error.
+ */
+int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order)
+{
+       int psize;
+
+       if (!buffer || order < 0)
+               return -EINVAL;
+
+       if (buffer->subbuf_order == order)
+               return 0;
+
+       psize = (1 << order) * PAGE_SIZE;
+       if (psize <= BUF_PAGE_HDR_SIZE)
+               return -EINVAL;
+
+       buffer->subbuf_order = order;
+       buffer->subbuf_size = psize - BUF_PAGE_HDR_SIZE;
+
+       /* Todo: reset the buffer with the new page size */
+
+       return 0;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_subbuf_order_set);
+
 /*
  * We only allocate new buffers, never free them if the CPU goes down.
  * If we were to free the buffer, then the user would lose any trace that was in

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 76dd0a4c8cb5e6813e3dc638fbffc7d80ac867e2..a010aba4c4a430d2cc351a9647720f87e933b929 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -9358,6 +9358,51 @@ static const struct file_operations buffer_percent_fops = {
        .llseek         = default_llseek,
 };
 
+static ssize_t
+buffer_order_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 = sprintf(buf, "%d\n", ring_buffer_subbuf_order_get(tr->array_buffer.buffer));
+
+       return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
+}
+
+static ssize_t
+buffer_order_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;
+
+       /* limit between 1 and 128 system pages */
+       if (val < 0 || val > 7)
+               return -EINVAL;
+
+       ret = ring_buffer_subbuf_order_set(tr->array_buffer.buffer, val);
+       if (ret)
+               return ret;
+
+       (*ppos)++;
+
+       return cnt;
+}
+
+static const struct file_operations buffer_order_fops = {
+       .open           = tracing_open_generic_tr,
+       .read           = buffer_order_read,
+       .write          = buffer_order_write,
+       .release        = tracing_release_generic_tr,
+       .llseek         = default_llseek,
+};
+
 static struct dentry *trace_instance_dir;
 
 static void
@@ -9824,6 +9869,9 @@ init_tracer_tracefs(struct trace_array *tr, struct dentry *d_tracer)
        trace_create_file("buffer_percent", TRACE_MODE_WRITE, d_tracer,
                        tr, &buffer_percent_fops);
 
+       trace_create_file("buffer_subbuf_order", TRACE_MODE_WRITE, d_tracer,
+                         tr, &buffer_order_fops);
+
        create_trace_options_dir(tr);
 
 #ifdef CONFIG_TRACER_MAX_TRACE