RE: [PATCH v5 02/15] ring-buffer: Page size per ring buffer

[David Laight]

From: Steven Rostedt
> Sent: 19 December 2023 18:54
> From: "Tzvetomir Stoyanov (VMware)" <tz.stoyanov@xxxxxxxxx>
> 
> Currently the size of one sub buffer page is global for all buffers and
> it is hard coded to one system page. In order to introduce configurable
> ring buffer sub page size, the internal logic should be refactored to
> work with sub page size per ring buffer.
> 
...
> -	nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
> +	/* Default buffer page size - one system page */
> +	buffer->subbuf_size = PAGE_SIZE - BUF_PAGE_HDR_SIZE;
> +
> +	/* Max payload is buffer page size - header (8bytes) */
> +	buffer->max_data_size = buffer->subbuf_size - (sizeof(u32) * 2);
> +
> +	nr_pages = DIV_ROUND_UP(size, buffer->subbuf_size);

While not new, does this really make any sense for systems with 64k pages?
Wouldn't it be better to have units of 4k?

...
> @@ -5102,14 +5110,14 @@ unsigned long ring_buffer_size(struct trace_buffer *buffer, int cpu)
>  {
>  	/*
>  	 * Earlier, this method returned
> -	 *	BUF_PAGE_SIZE * buffer->nr_pages
> +	 *	buffer->subbuf_size * buffer->nr_pages
>  	 * Since the nr_pages field is now removed, we have converted this to
>  	 * return the per cpu buffer value.

Overenthusiastic global replace...

	David

-
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