From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (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 79CD718AF9 for ; Fri, 22 Sep 2023 07:47:48 +0000 (UTC) Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C3C04180; Fri, 22 Sep 2023 00:47:46 -0700 (PDT) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id 8546021954; Fri, 22 Sep 2023 07:47:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1695368865; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=nCHJWLXY/1YrhTqt01qtJc1B4rW5IBdeEn9ZMU0RfFM=; b=S1J6FzTlABeg7deK/pGJfYJx9Ymmo3k9fUPr9VivC/k8RORz8OkEYiQpTHfo1jZwG2HKKf 7jAKPBYWtI6PUFnXvZNahHP7l/8ahMCv4YnhlGT3U3PGkbJ1zPfwEGH/dEjK4rTuLRu3Vc 2F6VxtnpW05sqoRVxUXElGF6pnBjbes= Received: from suse.cz (pmladek.udp.ovpn2.prg.suse.de [10.100.201.202]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id A7E482C142; Fri, 22 Sep 2023 07:47:44 +0000 (UTC) Date: Fri, 22 Sep 2023 09:47:44 +0200 From: Petr Mladek To: Enlin Mu Cc: John Ogness , Enlin Mu , rostedt@goodmis.org, senozhatsky@chromium.org, keescook@chromium.org, tony.luck@intel.com, gpiccoli@igalia.com, enlin.mu@unisoc.com, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH] printk: add cpu id information to printk() output Message-ID: References: <8734zfx2bo.fsf@jogness.linutronix.de> Precedence: bulk X-Mailing-List: linux-hardening@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Spam-Status: No, score=-4.4 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_MED,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net On Fri 2023-09-22 15:34:44, Enlin Mu wrote: > John Ogness 于2023年9月15日周五 16:34写道： > > > > On 2023-09-15, Enlin Mu wrote: > > > Sometimes we want to print cpu id of printk() messages to consoles > > > > > > diff --git a/include/linux/threads.h b/include/linux/threads.h > > > index c34173e6c5f1..6700bd9a174f 100644 > > > --- a/include/linux/threads.h > > > +++ b/include/linux/threads.h > > > @@ -34,6 +34,9 @@ > > > #define PID_MAX_LIMIT (CONFIG_BASE_SMALL ? PAGE_SIZE * 8 : \ > > > (sizeof(long) > 4 ? 4 * 1024 * 1024 : PID_MAX_DEFAULT)) > > > > > > +#define CPU_ID_SHIFT 23 > > > +#define CPU_ID_MASK 0xff800000 > > > > This only supports 256 CPUs. I think it doesn't make sense to try to > > squish CPU and Task IDs into 32 bits. > > > > What about introducing a caller_id option to always only print the CPU > > ID? Or do you really need Task _and_ CPU? > > Yes, I need it. > For SOC manufacturer, sometimes cpu is not stable, we need some debug > tools for this exceptions. > When an exception occurs, we may not be able to detect it in a timely > manner, but through Task _and_ CPU, we can roughly locate the CPU at > the time of the exception. Would frace be enough in this case? It has already been suggested earlier. The problem is that adding CPU into would require changes in the metadata stored in the ring buffer. And it would require updating userspace tools which read the log from a crash dump. It means that such a feature would need a lot of effort. And I would prefer to avoid it when there is another solution. If you debug the problem by adding extra printk messages you might also print the current CPU in the debug messages. Best Regards, Petr