From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4BDC63D62 for ; Fri, 19 Jul 2024 14:32:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721399541; cv=none; b=eBIalnJ6zpwe/7YxPXd6yQe4ecfTINaNl5C9uJeiP01+6Drronnaby6TLux6dOd6+V7QMcVXOw+izEYjmch695LqBD2qLfwV2HKgzpzb2CR9c0noRNu2XACI8Bs/S+lYLZ+gtNc6ZZr7OGbI4cMsZSZ/1vv0QnW3+FSsHQIFdDQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721399541; c=relaxed/simple; bh=H0/pVJkUPBAloJUYHyhfiIj/4kICO5yYgHMXhRxQV8M=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=PPuLBgjaCJZ2Q0KBBo81SaGPqjZWjGVSCRRGRtVap8QkkBAwoay8ckISz0KN+QCmunbddEXPu7UYxvMKINHqdXjnP4YGnUlSXuZ58hiknlkry7PzPmBvn+Ev8E30h5BcJ8vSnIFL8U3W+W+gpDhwN8ItBqmKjR12Vj+NLday/qs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0FE43C32782; Fri, 19 Jul 2024 14:32:19 +0000 (UTC) Date: Fri, 19 Jul 2024 10:32:18 -0400 From: Steven Rostedt To: Mathieu Desnoyers Cc: Linus Torvalds , LKML , Masami Hiramatsu , Dan Carpenter , Thorsten Blum Subject: Re: [GIT PULL] ring-buffer: Updates for 6.11 Message-ID: <20240719103218.6c1eedfc@rorschach.local.home> In-Reply-To: References: <20240716155118.152dea35@rorschach.local.home> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Tue, 16 Jul 2024 16:05:26 -0400 Mathieu Desnoyers wrote: > On 2024-07-16 15:51, Steven Rostedt wrote: > > > > > > Linus, > > > > tracing/ring-buffer: Have persistent buffer across reboots > > Hi Steven, > > Perhaps I'm missing something here, but we discussed previously that > you would document the fact that users of this feature are expected > to run the same kernel before/after reboot. > > Looking at this PR, I fail to find that documentation, or in fact > any documentation at all. Is this something that was overlooked ? So I went to update this, and realized there's no place that actually mentions anything about this being used across reboots (besides in the change logs). The only documentation is in kernel-parameters.txt: If memory has been reserved (see memmap for x86), the instance can use that memory: memmap=12M$0x284500000 trace_instance=boot_map@0x284500000:12M The above will create a "boot_map" instance that uses the physical memory at 0x284500000 that is 12Megs. The per CPU buffers of that instance will be split up accordingly. I do plan on adding more documentation on the use cases of this, but I was planning on doing that in the next merge window when the reserve_mem kernel parameter can be used. Right now, we only document what it does, and not what it is used for. Do you still have an issue with that part missing? No where does it mention that this is used across boots. There is a file created in the boot mapped instance directory that hints to the usage (last_boot_info), but still there's no assumptions made. In other words, why document a restriction on something that hasn't been documented? -- Steve