From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751019AbeEBI0Z (ORCPT ); Wed, 2 May 2018 04:26:25 -0400 Received: from foss.arm.com ([217.140.101.70]:54824 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750800AbeEBI0V (ORCPT ); Wed, 2 May 2018 04:26:21 -0400 Subject: Re: [PATCH v2 21/27] coresight: Convert driver messages to dev_dbg To: Kim Phillips , Suzuki K Poulose Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, mathieu.poirier@linaro.org, mike.leach@linaro.org, mark.rutland@arm.com, will.deacon@arm.com, robin.murphy@arm.com, sudeep.holla@arm.com, frowand.list@gmail.com, robh@kernel.org, john.horley@arm.com References: <1525165857-11096-1-git-send-email-suzuki.poulose@arm.com> <1525165857-11096-22-git-send-email-suzuki.poulose@arm.com> <20180501225503.a55fb963795afb40163f3763@arm.com> From: Robert Walker Message-ID: <019a4703-f51a-b402-7e92-c5045a17361a@arm.com> Date: Wed, 2 May 2018 09:25:38 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: <20180501225503.a55fb963795afb40163f3763@arm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/05/18 04:55, Kim Phillips wrote: > On Tue, 1 May 2018 10:10:51 +0100 > Suzuki K Poulose wrote: > >> Convert component enable/disable messages from dev_info to dev_dbg. >> This is required to prevent LOCKDEP splats when operating in perf >> mode where we could be called with locks held to enable a coresight > Can we see the splats? Doesn't lockdep turn itself off if it starts > triggering too many splats? > >> path. If someone wants to really see the messages, they can always >> enable it at runtime via dynamic_debug. > Won't the splats still occur when the messages are enabled with > dynamic_debug? > > So in effect this patch only tries to mitigate the splats, all the > while making things harder for regular users that now have to recompile > their kernels, in exchange for a very small convenience for kernel > developers that happen to see a splat or two with DEBUG_LOCKDEP set? > > Not the greatest choice...How about moving the dev_infos outside of the > locks instead? > > Thanks, > > Kim The other reason for making these dev_dbg is performance - a message is output each time a source / link / sink is enabled or disabled, so we can get 20+ messages on each process switch when tracing with perf.  This has a significant effect on the runtime of the application being traced. Regards Rob