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[83.52.55.163]) by smtp.gmail.com with ESMTPSA id 19sm1439970wmo.39.2021.08.24.00.29.31 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 24 Aug 2021 00:29:32 -0700 (PDT) Subject: Re: [PATCH v7 05/15] machine: Improve the error reporting of smp parsing To: "wangyanan (Y)" , qemu-devel@nongnu.org, Eduardo Habkost , Igor Mammedov References: <20210823122804.7692-1-wangyanan55@huawei.com> <20210823122804.7692-6-wangyanan55@huawei.com> <4b49fb0c-ec73-d8ca-f622-cc8e21ed0140@huawei.com> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Message-ID: Date: Tue, 24 Aug 2021 09:29:31 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <4b49fb0c-ec73-d8ca-f622-cc8e21ed0140@huawei.com> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=philmd@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=philmd@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -55 X-Spam_score: -5.6 X-Spam_bar: ----- X-Spam_report: (-5.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.743, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-2.023, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Maydell , Andrew Jones , =?UTF-8?Q?Daniel_P_=2e_Berrang=c3=a9?= , Pierre Morel , "Michael S . Tsirkin" , Cornelia Huck , Richard Henderson , Greg Kurz , Halil Pasic , Paolo Bonzini , Pankaj Gupta , Thomas Huth , wanghaibin.wang@huawei.com, David Gibson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 8/24/21 6:51 AM, wangyanan (Y) wrote: > On 2021/8/23 21:17, Philippe Mathieu-Daudé wrote: >> On 8/23/21 2:27 PM, Yanan Wang wrote: >>> We have two requirements for a valid SMP configuration: >>> the product of "sockets * cores * threads" must represent all the >>> possible cpus, i.e., max_cpus, and then must include the initially >>> present cpus, i.e., smp_cpus. >>> >>> So we only need to ensure 1) "sockets * cores * threads == maxcpus" >>> at first and then ensure 2) "maxcpus >= cpus". With a reasonable >>> order of the sanity check, we can simplify the error reporting code. >>> When reporting an error message we also report the exact value of >>> each topology member to make users easily see what's going on. >>> >>> Signed-off-by: Yanan Wang >>> Reviewed-by: Andrew Jones >>> Reviewed-by: Pankaj Gupta >>> --- >>>   hw/core/machine.c | 22 +++++++++------------- >>>   hw/i386/pc.c      | 24 ++++++++++-------------- >>>   2 files changed, 19 insertions(+), 27 deletions(-) >>> >>> diff --git a/hw/core/machine.c b/hw/core/machine.c >>> index 85908abc77..093c0d382d 100644 >>> --- a/hw/core/machine.c >>> +++ b/hw/core/machine.c >>> @@ -779,25 +779,21 @@ static void smp_parse(MachineState *ms, >>> SMPConfiguration *config, Error **errp) >>>       maxcpus = maxcpus > 0 ? maxcpus : sockets * cores * threads; >>>       cpus = cpus > 0 ? cpus : maxcpus; >>>   -    if (sockets * cores * threads < cpus) { >>> -        error_setg(errp, "cpu topology: " >>> -                   "sockets (%u) * cores (%u) * threads (%u) < " >>> -                   "smp_cpus (%u)", >>> -                   sockets, cores, threads, cpus); >>> +    if (sockets * cores * threads != maxcpus) { >>> +        error_setg(errp, "Invalid CPU topology: " >>> +                   "product of the hierarchy must match maxcpus: " >>> +                   "sockets (%u) * cores (%u) * threads (%u) " >>> +                   "!= maxcpus (%u)", >>> +                   sockets, cores, threads, maxcpus); >>>           return; >>>       } >> Thinking about scalability, MachineClass could have a >> parse_cpu_topology() handler, and this would be the >> generic one. Principally because architectures don't >> use the same terms, and die/socket/core/thread arrangement >> is machine specific (besides being arch-spec). >> Not a problem as of today, but the way we try to handle >> this generically seems over-engineered to me. > Hi Philippe, > > The reason for introducing a generic implementation and avoiding > specific ones is that we thought there is little difference in parsing > logic between the specific parsers. Most part of the parsing is the > automatic calculation of missing values and the related error reporting, > in which the only difference between parsers is the handling of specific > (no matter of arch-specific or machine-specifc) parameters. > > So it may be better to keep the parsing logic unified if we can easily > realize that. And actually we can use compat stuff to handle specific > topology parameters well. See implementation in patch #10. > > There have been patches on list introducing new specific members > (s390 related in [1] and ARM related in [2]), and in each of them there > is a specific parser needed. However, based on generic one we can > extend without the increasing code duplication. > > There is also some discussion about generic/specific parser in [1], > which can be a reference. > > [1] > https://lore.kernel.org/qemu-devel/1626281596-31061-2-git-send-email-pmorel@linux.ibm.com/ > > [2] > https://lore.kernel.org/qemu-devel/20210516103228.37792-1-wangyanan55@huawei.com/ OK I read Daniel's rationale here: https://lore.kernel.org/qemu-devel/YPFN83pKBt7F97kW@redhat.com/ Thanks, Phil.