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Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.1 Subject: Re: [PATCH] target/ppc/cpu-models: Update max alias to power10 Content-Language: en-US To: Greg Kurz , Thomas Huth Cc: Murilo Opsfelder Araujo , qemu-devel@nongnu.org, qemu-ppc@nongnu.org, =?UTF-8?Q?C=c3=a9dric_Le_Goater?= , David Gibson , mopsfelder@gmail.com, =?UTF-8?Q?Daniel_P_=2e_Berrang=c3=a9?= , Fabiano Rosas References: <20220531172711.94564-1-muriloo@linux.ibm.com> <475c2f40-8c58-8d51-4cc5-da5b9db814f2@redhat.com> <20220601103825.498c378f@bahia> <5076ea8a-428d-5aa2-1a8c-cd38bf67c7f9@redhat.com> <20220601120324.66c77571@bahia> From: Daniel Henrique Barboza In-Reply-To: <20220601120324.66c77571@bahia> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2001:4860:4864:20::2a; envelope-from=danielhb413@gmail.com; helo=mail-oa1-x2a.google.com X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_ENVFROM_END_DIGIT=0.25, FREEMAIL_FROM=0.001, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 6/1/22 07:03, Greg Kurz wrote: > On Wed, 1 Jun 2022 11:25:43 +0200 > Thomas Huth wrote: > >> On 01/06/2022 10.38, Greg Kurz wrote: >>> On Wed, 1 Jun 2022 09:27:31 +0200 >>> Thomas Huth wrote: >>> >>>> On 31/05/2022 19.27, Murilo Opsfelder Araujo wrote: >>>>> Update max alias to power10 so users can take advantage of a more >>>>> recent CPU model when '-cpu max' is provided. >> ... >>> We already have the concept of default CPU for the spapr >>> machine types, that is usually popped up to the newer >>> CPU model that is going to be supported in production. >>> This goes with a bump of the machine type version as >>> well for the sake of migration. This seems a lot more >>> reliable than the "max" thingy IMHO. >>> >>> Unless there's a very important use case I'm missing, >>> I'd rather kill the thing instead of trying to resurrect >>> it. >> >> It's about making ppc similar to other architectures, which >> have "-cpu max" as well, see: >> >> https://gitlab.com/qemu-project/qemu/-/issues/1038 >> >> It would be nice to get something similar on ppc. >> > > Problem is that on ppc, given the variety of models and boards, > the concept of "max" is quite fuzzy... i.e. a lot of cases to > consider for a benefit that is unclear to me. Hence my questioning. > If the idea is just to match what other targets do without a specific > use case in mind, this looks quite useless to me. I mean, yes, the use case is that users/tooling are using -cpu max with x86 and arm. We'd rather not increase the gap between them and ppc64 because we ended up removing -cpu max. Even if the concept might not be applicable to every machine we have we can alias -cpu max to the default machine CPU. > >> By the way, the warnings that you currently get when running with >> TCG are quite ugly, too: >> >> $ ./qemu-system-ppc64 >> qemu-system-ppc64: warning: TCG doesn't support requested feature, >> cap-cfpc=workaround >> qemu-system-ppc64: warning: TCG doesn't support requested feature, >> cap-sbbc=workaround >> qemu-system-ppc64: warning: TCG doesn't support requested feature, >> cap-ibs=workaround >> qemu-system-ppc64: warning: TCG doesn't support requested feature, >> cap-ccf-assist=on >> >> Maybe these could get fixed with a proper "max" CPU in TCG >> mode, too? >> > > I don't think so. These warnings are the consequence of pseries > being the default machine for ppc64, and the default pseries > machine decides on the default CPU model and default values for > features (in this case, these are mitigations for spectre/meltdown). > TCG doesn't support them but we certainly don't want to add more > divergence between TCG and KVM. I sent a patch last year trying to suppress the warning: https://lists.gnu.org/archive/html/qemu-devel/2021-01/msg05029.html I proposed to suppress these warnings when the user didn't specifically set those caps to true (which TCG doesn't support). David thought that this was also a bad idea and we reached an impasse. Back then seemed like I was the only one severely aggravated by these messages so I gave up :) Thanks, Daniel > > Cheers, > > -- > Greg > >> Thomas >> >