From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3zg6cG1jlWzDqBn for ; Tue, 13 Feb 2018 00:54:53 +1100 (AEDT) Received: from pps.filterd (m0098417.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w1CDrmTC024081 for ; Mon, 12 Feb 2018 08:54:51 -0500 Received: from e06smtp12.uk.ibm.com (e06smtp12.uk.ibm.com [195.75.94.108]) by mx0a-001b2d01.pphosted.com with ESMTP id 2g38yxfxj0-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Mon, 12 Feb 2018 08:54:51 -0500 Received: from localhost by e06smtp12.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 12 Feb 2018 13:54:49 -0000 Subject: Re: [PATCH 2/3] cxl: Introduce module parameter 'enable_psltrace' To: Vaibhav Jain , christophe lombard , linuxppc-dev@lists.ozlabs.org Cc: Philippe Bergheaud , "Alastair D'Silva" , Christophe Lombard , Andrew Donnellan References: <20180209042535.16845-1-vaibhav@linux.vnet.ibm.com> <20180209042535.16845-3-vaibhav@linux.vnet.ibm.com> <87a7wf4flx.fsf@vajain21.in.ibm.com> From: Frederic Barrat Date: Mon, 12 Feb 2018 14:54:45 +0100 MIME-Version: 1.0 In-Reply-To: <87a7wf4flx.fsf@vajain21.in.ibm.com> Content-Type: text/plain; charset=utf-8; format=flowed Message-Id: <51364d03-d7a5-471b-2531-cf4c17af8c8d@linux.vnet.ibm.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Le 11/02/2018 à 18:10, Vaibhav Jain a écrit : > Thanks for reviewing the patch Christophe, > > christophe lombard writes: >>> +bool cxl_enable_psltrace = true; >>> +module_param_named(enable_psltrace, cxl_enable_psltrace, bool, 0600); >>> +MODULE_PARM_DESC(enable_psltrace, "Set PSL traces on probe. default: on"); >>> + >> I am not too agree to add a new parameter. This can cause doubts. >> PSL team has confirmed that enabling traces has no impact. >> Do you see any reason to disable the traces ? > > Traces on PSL follow a 'set and fetch' model. So once the trace buffer for > a specific array is full it will stop and switch to 'FIN' state and at > that point we need to fetch the trace-data and reinit the array to > re-arm it. If the PSL trace arrays don't wrap, is there anything to gain by enabling tracing by default instead of letting the developer handle it through sysfs? I was under the (now wrong) impression that the PSL would wrap. I'm not a big fan of the module parameter. It seems we're giving a second way of activating traces on top of sysfs, more cumbersome and limited. Fred > There might be some circumstances where this model may lead to confusion > specifically when AFU developers assume that the trace arrays are > already armed and dont re-arm it causing miss of trace data. > > So this module param is a compromise to keep the old behaviour of traces > array intact where in the arming/disarming of the trace arrays is > controlled completely by userspace tooling and not by cxl. >