From: Steven Rostedt <rostedt@goodmis.org>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org,
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 10:38:44 -0500 [thread overview]
Message-ID: <20231210103844.7cabaa13@gandalf.local.home> (raw)
In-Reply-To: <76797ddd-bb87-4af9-9703-1ec00a0d318c@efficios.com>
On Sun, 10 Dec 2023 09:17:44 -0500
Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote:
> 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. I actually agree with you and thought about doing just that, but
decided to not make those changes and send out these patches with the
given API first. I wanted to see if you would comment on this ;-) You did
not disappoint!
I was thinking of keeping the same kind of interface as we have with the
buffer size "buffer_size_kb", and have it be "buffer_subbuf_size_kb", where
you specify the minimum size in kilobytes and it creates it, and the subbuf
may end up being bigger than specified (as that's more a implementation
detail).
Now that you called it out, I will add a patch to convert that as such. But
will keep the current patches in for historical reasons.
-- Steve
prev parent reply other threads:[~2023-12-10 15:38 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 ` [PATCH 00/14] ring-buffer/tracing: Allow ring buffer to have bigger sub buffers Mathieu Desnoyers
2023-12-10 15:38 ` Steven Rostedt [this message]
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