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From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: Steven Rostedt <rostedt@goodmis.org>,
	linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Tzvetomir Stoyanov <tz.stoyanov@gmail.com>,
	Vincent Donnefort <vdonnefort@google.com>,
	Kent Overstreet <kent.overstreet@gmail.com>
Subject: Re: [PATCH 00/14] ring-buffer/tracing: Allow ring buffer to have bigger sub buffers
Date: Sun, 10 Dec 2023 09:17:44 -0500	[thread overview]
Message-ID: <76797ddd-bb87-4af9-9703-1ec00a0d318c@efficios.com> (raw)
In-Reply-To: <20231210035404.053677508@goodmis.org>

On 2023-12-09 22:54, Steven Rostedt wrote:
[...]
> 
> Basically, events to the tracing subsystem are limited to just under a
> PAGE_SIZE, as the ring buffer is split into "sub buffers" of one page
> size, and an event can not be bigger than a sub buffer. This allows users
> to change the size of a sub buffer by the order:
> 
>    echo 3 > /sys/kernel/tracing/buffer_subbuf_order
> 
> Will make each sub buffer a size of 8 pages, allowing events to be almost
> as big as 8 pages in size (sub buffers do have meta data on them as
> well, keeping an event from reaching the same size as a sub buffer).

Specifying the "order" of subbuffer size as a power of two of
number of pages is a poor UX choice for a user-facing ABI.

I would recommend allowing the user to specify the size in bytes, and
internally bump to size to the next power of 2, with a minimum of
PAGE_SIZE.

Thanks,

Mathieu


-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com


  parent reply	other threads:[~2023-12-10 14:17 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-12-10  3:54 [PATCH 00/14] ring-buffer/tracing: Allow ring buffer to have bigger sub buffers Steven Rostedt
2023-12-10  3:54 ` [PATCH 01/14] ring-buffer: Refactor ring buffer implementation Steven Rostedt
2023-12-10  3:54 ` [PATCH 02/14] ring-buffer: Page size per ring buffer Steven Rostedt
2023-12-10  3:54 ` [PATCH 03/14] ring-buffer: Add interface for configuring trace sub buffer size Steven Rostedt
2023-12-10  3:54 ` [PATCH 04/14] ring-buffer: Set new size of the ring buffer sub page Steven Rostedt
2023-12-10  3:54 ` [PATCH 05/14] ring-buffer: Read and write to ring buffers with custom sub buffer size Steven Rostedt
2023-12-10  3:54 ` [PATCH 06/14] ring-buffer: Clear pages on error in ring_buffer_subbuf_order_set() failure Steven Rostedt
2023-12-10  3:54 ` [PATCH 07/14] ring-buffer: Do no swap cpu buffers if order is different Steven Rostedt
2023-12-10  3:54 ` [PATCH 08/14] ring-buffer: Make sure the spare sub buffer used for reads has same size Steven Rostedt
2023-12-10  3:54 ` [PATCH 09/14] tracing: Update snapshot order along with main buffer order Steven Rostedt
2023-12-10  3:54 ` [PATCH 10/14] tracing: Stop the tracing while changing the ring buffer subbuf size Steven Rostedt
2023-12-10  3:54 ` [PATCH 11/14] ring-buffer: Keep the same size when updating the order Steven Rostedt
2023-12-10  3:54 ` [PATCH 12/14] ring-buffer: Just update the subbuffers when changing their allocation order Steven Rostedt
2023-12-10  3:54 ` [PATCH 13/14] ring-buffer: Add documentation on the buffer_subbuf_order file Steven Rostedt
2023-12-10 14:28   ` Mathieu Desnoyers
2023-12-10  3:54 ` [PATCH 14/14] ringbuffer/selftest: Add basic selftest to test chaning subbuf order Steven Rostedt
2023-12-10 14:26   ` Mathieu Desnoyers
2023-12-10 15:44     ` Steven Rostedt
2023-12-10 14:17 ` Mathieu Desnoyers [this message]
2023-12-10 15:38   ` [PATCH 00/14] ring-buffer/tracing: Allow ring buffer to have bigger sub buffers Steven Rostedt

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