Hi, Richard. Thank you for your comment.
> My first thought is that -cpu max can simply enable the extensions, without > extra flags. The max cpu has all of the features that we can enable, and as I > see it this is just one more. Let me confirm a few things about the above comment. Does it mean that I don't need to explicitly enable individual extensions such as a64fx-hpc-sec, a64fx-hpc-hwpf, and a64fx-hpc-hwb, since all extensions can be enabled by specifying -cpu max? > The microarchitectural document provided does not list all of the system > register reset values for the A64FX, and I would be surprised if there were an > architectural id register that specified a non-standard extension like this. > Thus I would expect to add ARM_FEATURE_A64FX with which to enable these > extensions in helper.c. As you said, some of the published specifications do not describe the reset values of the registers. I would like to implement this in QEMU by referring to a real machine with A64FX. > I can certainly help you with this. I am not familiar with this, and I apologize for any inconvenience this may cause, but I appreciate your cooperation. Best regards. > -----Original Message----- > From: Richard Henderson <richard.hender...@linaro.org> > Sent: Thursday, June 3, 2021 4:02 AM > To: Peter Maydell <peter.mayd...@linaro.org>; Ishii, Shuuichirou/石井 周一郎 > <ishii.shuuic...@fujitsu.com> > Cc: qemu-...@nongnu.org; qemu-devel@nongnu.org > Subject: Re: [RFC] Adding the A64FX's HPC funtions. > > On 6/1/21 8:21 AM, Peter Maydell wrote: > >>> I'm thinking of implementing A64FX HPC extension in qemu. > >>> A64FX [1] is a CPU developed by Fujitsu that implements armv8+SVE. > >>> > >>> [1] > >>> > https://github.com/fujitsu/A64FX/blob/master/doc/A64FX_Microarchitec > >>> ture > >>> _Manual_en_1.4.pdf > >>> > >>> A64FX is a CPU developed for HPC (High Performance Computing), and > >>> HPC extensions [2] are implemented to improve the performance of user > programs. > >>> > >>> [2] > >>> > https://github.com/fujitsu/A64FX/blob/master/doc/A64FX_Specification > >>> _HP > >>> C_Extension_v1_EN.pdf > >>> > >>> The details of each function are described in [2], and the HPC > >>> extensions include > >>> 1) Tag address override > >>> 2) Sector cache > >>> 3) Hardware barrier > >>> 4) Hardware prefetch assist > >>> are implemented. > > Thanks for the pointers. It looks to me that it'll be easy to implement > these in > qemu. We'll need to implement the registers, so that the OS can read back the > values, but we do not need to actually do anything with them. > > >>> 1) Is target/arm/helper.c enough to implement the register > >>> (ARMCPRegInfo > >>> structure) of HPC extension function of A64FX? > > Yes. > > >>> 2) Is it OK to specify the option to set the HPC extension of A64FX > >>> as follows, for example? > >>> > >>> -M virt -cpu max,a64fx-hpc-sec=on (*sector cache function) -M virt > >>> -cpu max,a64fx-hpc-hwpf=on (*hardware prefetvh assist function) -M > >>> virt -cpu max,a64fx-hpc-hwb=on (*hardware barrier function) > >>> > >>> It is also possible to implement something like -cpu a64fx, but > >>> since we don't know if we can implement it immediately, we assume > >>> that we will use the -cpu max option first. > > My first thought is that -cpu max can simply enable the extensions, without > extra flags. The max cpu has all of the features that we can enable, and as I > see it this is just one more. > > I would like to add -cpu a64fx at some point. But as you say, that need not > happen right away. > > >>> Since there is no example of A64FX function implemented in QEMU, we > >>> would appreciate your comments before we post a patch. > > We endeavor to enable features by the architectural id registers when > possible. > Thus the cpu_isar_feature() checks in helper.c. > > The microarchitectural document provided does not list all of the system > register reset values for the A64FX, and I would be surprised if there were an > architectural id register that specified a non-standard extension like this. > Thus I would expect to add ARM_FEATURE_A64FX with which to enable these > extensions in helper.c. > > I can certainly help you with this. > > > r~
