On Wed, 17 Nov 2021 17:41:00 +0200
"Tzvetomir Stoyanov (VMware)" <tz.stoyanov@xxxxxxxxx> wrote:
> The trace ring buffer page size can be configured, per trace instance. A
> new ftrace file "buffer_page_size" is added to get and set the size of
> the ring buffer page for current trace instance. The size must be
> multiple of system page size, that's why the new interface works with
> system page count, instead of absolute page size: 1 means the ring
> buffer page is equal to one system page and so forth. The ring buffer
> page is limited between 1 and 100 system pages.
It should be an order of pages, not a size (or a multiple).
0 - 1 page
1 - 2 pages
2 - 4 pages
3 - 8 pages
4 - 16 pages
[..]
>
> Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@xxxxxxxxx>
> ---
> include/linux/ring_buffer.h | 3 +++
> kernel/trace/ring_buffer.c | 51 +++++++++++++++++++++++++++++++++++++
> kernel/trace/trace.c | 47 ++++++++++++++++++++++++++++++++++
> 3 files changed, 101 insertions(+)
>
> diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
> index d9a2e6e8fb79..53cd7a38b717 100644
> --- a/include/linux/ring_buffer.h
> +++ b/include/linux/ring_buffer.h
> @@ -202,6 +202,9 @@ 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_page_size_get(struct trace_buffer *buffer);
> +int ring_buffer_page_size_set(struct trace_buffer *buffer, int psize);
ring_buffer_subbuf_order_get/set()
> +
> enum ring_buffer_flags {
> RB_FL_OVERWRITE = 1 << 0,
> };
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index 6bca2977ca1a..9aa245795c3d 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -5677,6 +5677,57 @@ int ring_buffer_read_page(struct trace_buffer *buffer,
> }
> EXPORT_SYMBOL_GPL(ring_buffer_read_page);
>
> +/**
> + * ring_buffer_page_size_get - get count of system pages in one buffer page.
> + * @buffer: The ring_buffer to get the system page count from
> + *
> + * By default, one ring buffer pages equals to one system page. This parameter
> + * is configurable, per ring buffer. The size of the ring buffer page can be
> + * extended, but must be multiple of system page size.
> + *
> + * Returns the size of buffer page, in system pages: 1 means the buffer size is
> + * one system page and so forth. In case of an error < 0 is returned.
> + */
> +int ring_buffer_page_size_get(struct trace_buffer *buffer)
> +{
> + if (!buffer)
> + return -EINVAL;
> +
> + return (buffer->page_size + BUF_PAGE_HDR_SIZE) / PAGE_SIZE;
And save it to another field in the structure, and not calculate it.
> +}
> +EXPORT_SYMBOL_GPL(ring_buffer_page_size_get);
> +
> +/**
> + * ring_buffer_page_size_set - set the size of ring buffer page.
> + * @buffer: The ring_buffer to set the new page size.
> + * @pcount: Number of system pages.
> + *
> + * 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 multiple of
> + * system page size, that's why the input parameter @pcount is the count of
> + * system pages that are allocated for one ring buffer page.
> + *
> + * Returns 0 on success or < 0 in case of an error.
> + */
> +int ring_buffer_page_size_set(struct trace_buffer *buffer, int pcount)
> +{
> + int psize;
> +
> + if (!buffer)
> + return -EINVAL;
> +
> + psize = pcount * PAGE_SIZE;
> + if (psize <= BUF_PAGE_HDR_SIZE)
> + return -EINVAL;
> +
> + buffer->page_size = psize - BUF_PAGE_HDR_SIZE;
> +
> + /* Todo: reset the buffer with the new page size */
> +
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(ring_buffer_page_size_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 f9139dc1262c..05fc2712fdbd 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -9005,6 +9005,50 @@ static const struct file_operations buffer_percent_fops = {
> .llseek = default_llseek,
> };
>
> +static ssize_t
> +buffer_psize_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_page_size_get(tr->array_buffer.buffer));
> +
> + return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
> +}
> +
> +static ssize_t
> +buffer_psize_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 < 1 || val > 100)
> + return -EINVAL;
> +
> + ret = ring_buffer_page_size_set(tr->array_buffer.buffer, val);
> + if (ret)
> + return ret;
> +
> + (*ppos)++;
> +
> + return cnt;
> +}
> +
> +static const struct file_operations buffer_psize_fops = {
> + .open = tracing_open_generic_tr,
> + .read = buffer_psize_read,
> + .write = buffer_psize_write,
> + .release = tracing_release_generic_tr,
> + .llseek = default_llseek,
> +};
> +
> static struct dentry *trace_instance_dir;
>
> static void
> @@ -9458,6 +9502,9 @@ init_tracer_tracefs(struct trace_array *tr, struct dentry *d_tracer)
> trace_create_file("buffer_percent", TRACE_MODE_READ, d_tracer,
> tr, &buffer_percent_fops);
>
> + trace_create_file("buffer_page_size", TRACE_MODE_WRITE, d_tracer,
"buffer_subbuf_order"
-- Steve
> + tr, &buffer_psize_fops);
> +
> create_trace_options_dir(tr);
>
> trace_create_maxlat_file(tr, d_tracer);
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