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[70.114.203.196]) by smtp.gmail.com with ESMTPSA id gr15-20020a056870aa8f00b0021ff3548a19sm37620oab.37.2024.02.28.14.26.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 28 Feb 2024 14:26:59 -0800 (PST) From: John Groves X-Google-Original-From: John Groves Date: Wed, 28 Feb 2024 16:26:56 -0600 To: Dan Williams Cc: Shiju Jose , "linux-cxl@vger.kernel.org" , "linux-acpi@vger.kernel.org" , "linux-mm@kvack.org" , "dave@stgolabs.net" , Jonathan Cameron , "dave.jiang@intel.com" , "alison.schofield@intel.com" , "vishal.l.verma@intel.com" , "ira.weiny@intel.com" , "linux-edac@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "david@redhat.com" , "Vilas.Sridharan@amd.com" , "leo.duran@amd.com" , "Yazen.Ghannam@amd.com" , "rientjes@google.com" , "jiaqiyan@google.com" , "tony.luck@intel.com" , "Jon.Grimm@amd.com" , "dave.hansen@linux.intel.com" , "rafael@kernel.org" , "lenb@kernel.org" , "naoya.horiguchi@nec.com" , "james.morse@arm.com" , "jthoughton@google.com" , "somasundaram.a@hpe.com" , "erdemaktas@google.com" , "pgonda@google.com" , "duenwen@google.com" , "mike.malvestuto@intel.com" , "gthelen@google.com" , "wschwartz@amperecomputing.com" , "dferguson@amperecomputing.com" , tanxiaofei , "Zengtao (B)" , "kangkang.shen@futurewei.com" , wanghuiqiang , Linuxarm Subject: Re: [RFC PATCH v6 00/12] cxl: Add support for CXL feature commands, CXL device patrol scrub control and DDR5 ECS control features Message-ID: <7r4vrkmpma7u7zkzanuame7q4vl4ourygnyww4muzqjfvwvu3y@qkwmmoy6jflr> References: <20240215111455.1462-1-shiju.jose@huawei.com> <65d6936952764_1138c7294e@dwillia2-xfh.jf.intel.com.notmuch> <54c55412e9374e4e9cacf8410a5a98cb@huawei.com> <65d8f5201f8cc_2509b29467@dwillia2-mobl3.amr.corp.intel.com.notmuch> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <65d8f5201f8cc_2509b29467@dwillia2-mobl3.amr.corp.intel.com.notmuch> X-Rspam-User: X-Stat-Signature: xj6fx4975xteobqy85q9ahrdf4dzgnrp X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 66F354001D X-HE-Tag: 1709159221-986108 X-HE-Meta: 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 fumz+zLL 19EhbsiqKQuJHlMwA+mGaUo4CJ6zn/cYJkigi2PMtP4TcTUR2NgJ8byiADwB21FFfS8Ewlx14sPfuISyD3KhV4wSuPvQP5NUh/HlbL7BcNlAoTbUTIEnj4M2TYvMSIEiKOotNH5wGaytuALB9ME7xRmTNPBa8ITeXXcBIHUdAjT9I6BkN7k+w7O00Qyu8UNNXjboR4U6hnCYUJ3hE64KfCaMq3jufnaCRxudkny9bMPd7IKo= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000005, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 24/02/23 11:42AM, Dan Williams wrote: > Shiju Jose wrote: > > Hi Dan, > > > > Thanks for the feedback. > > > > Please find reply inline. > > > > >-----Original Message----- > > >From: Dan Williams > > >Sent: 22 February 2024 00:21 > > >To: Shiju Jose ; linux-cxl@vger.kernel.org; linux- > > >acpi@vger.kernel.org; linux-mm@kvack.org; dan.j.williams@intel.com; > > >dave@stgolabs.net; Jonathan Cameron ; > > >dave.jiang@intel.com; alison.schofield@intel.com; vishal.l.verma@intel.com; > > >ira.weiny@intel.com > > >Cc: linux-edac@vger.kernel.org; linux-kernel@vger.kernel.org; > > >david@redhat.com; Vilas.Sridharan@amd.com; leo.duran@amd.com; > > >Yazen.Ghannam@amd.com; rientjes@google.com; jiaqiyan@google.com; > > >tony.luck@intel.com; Jon.Grimm@amd.com; dave.hansen@linux.intel.com; > > >rafael@kernel.org; lenb@kernel.org; naoya.horiguchi@nec.com; > > >james.morse@arm.com; jthoughton@google.com; somasundaram.a@hpe.com; > > >erdemaktas@google.com; pgonda@google.com; duenwen@google.com; > > >mike.malvestuto@intel.com; gthelen@google.com; > > >wschwartz@amperecomputing.com; dferguson@amperecomputing.com; > > >tanxiaofei ; Zengtao (B) ; > > >kangkang.shen@futurewei.com; wanghuiqiang ; > > >Linuxarm ; Shiju Jose > > >Subject: RE: [RFC PATCH v6 00/12] cxl: Add support for CXL feature commands, > > >CXL device patrol scrub control and DDR5 ECS control features > > > > > >shiju.jose@ wrote: > > >> From: Shiju Jose > > >> > > >> 1. Add support for CXL feature mailbox commands. > > >> 2. Add CXL device scrub driver supporting patrol scrub control and ECS > > >> control features. > > >> 3. Add scrub subsystem driver supports configuring memory scrubs in the > > >system. > > >> 4. Register CXL device patrol scrub and ECS with scrub subsystem. > > >> 5. Add common library for RASF and RAS2 PCC interfaces. > > >> 6. Add driver for ACPI RAS2 feature table (RAS2). > > >> 7. Add memory RAS2 driver and register with scrub subsystem. > > > > > >I stepped away from this patch set to focus on the changes that landed for v6.8 > > >and the follow-on regression fixups. Now that v6.8 CXL work has quieted down > > >and I circle back to this set for v6.9 I find the lack of story in this cover letter to > > >be unsettling. As a reviewer I should not have to put together the story on why > > >Linux should care about this feature and independently build up the > > >maintainence-burden vs benefit tradeoff analysis. > > I will add more details to the cover letter. > > > > > > > >Maybe it is self evident to others, but for me there is little in these changelogs > > >besides "mechanism exists, enable it". There are plenty of platform or device > > >mechanisms that get specified that Linux does not enable for one reason or > > >another. > > > > > >The cover letter needs to answer why it matters, and what are the tradeoffs. > > >Mind you, in my submissions I do not always get this right in the cover letter [1], > > >but hopefully at least one of the patches tells the story [2]. > > > > > >In other words, imagine you are writing the pull request to Linus or someone > > >else with limited time who needs to make a risk decision on a pull request with a > > >diffstat of: > > > > > > 23 files changed, 3083 insertions(+) > > > > > >...where the easiest decision is to just decline. As is, these changelogs are not > > >close to tipping the scale to "accept". > > > > > >[sidebar: how did this manage to implement a new subsystem with 2 consumers > > >(CXL + ACPI), without modifying a single existing line? Zero deletions? That is > > >either an indication that Linux perfectly anticipated this future use case > > >(unlikely), or more work needs to be done to digest an integrate these concepts > > >into existing code paths] > > > > > >One of the first questions for me is why CXL and RAS2 as the first consumers and > > >not NVDIMM-ARS and/or RASF Patrol Scrub? Part of the maintenance burden > > We don't personally care about NVDIMMS but would welcome drivers from others. > > Upstream would also welcome consideration of maintenance burden > reduction before piling on, at least include *some* consideration of the > implications vs this response that comes off as "that's somebody else's > problem". > > > Regarding RASF patrol scrub no one cared about it as it's useless and > > any new implementation should be RAS2. > > The assertion that "RASF patrol scrub no one cared about it as it's > useless and any new implementation should be RAS2" needs evidence. > > For example, what platforms are going to ship with RAS2 support, what > are the implications of Linux not having RAS2 scrub support in a month, > or in year? There are parts of the ACPI spec that have never been > implemented what is the evidence that RAS2 is not going to suffer the > same fate as RASF? There are parts of the CXL specification that have > never been implemented in mass market products. > > > Previous discussions in the community about RASF and scrub could be find here. > > https://lore.kernel.org/lkml/20230915172818.761-1-shiju.jose@huawei.com/#r > > and some old ones, > > https://patchwork.kernel.org/project/linux-arm-kernel/patch/CS1PR84MB0038718F49DBC0FF03919E1184390@CS1PR84MB0038.NAMPRD84.PROD.OUTLOOK.COM/ > > > > Do not make people hunt for old discussions, if there are useful points > in that discussion that make the case for the patch set include those in > the next submission, don't make people hunt for the latest state of the > story. > > > https://lore.kernel.org/all/20221103155029.2451105-1-jiaqiyan@google.com/ > > Yes, now that is a useful changelog, thank you for highlighting it, > please follow its example. Just a comment that is not directed at the implementation details: at Micron we see demand for the scrub control feature, so we do hope to see this support go in sooner rather than later. Regards, John