Shiyou Yin <[email protected]> 于2020年2月22日周六 下午9:26写道： > > >-----Original Message----- > >From: Adam Jackson [mailto:[email protected]] > >Sent: Friday, February 21, 2020 11:33 PM > >To: Yin Shiyou; [email protected] > >Subject: Re: [Pixman] [PATCH v2 2/3] build: use '-mloongson-mmi' for > >Loongson MMI. > > > >On Thu, 2020-02-20 at 22:23 +0800, Yin Shiyou wrote: > >> It's suggested to use '-mloongson-mmi' to enable MMI. > >> To keep compatible with old processor, '-mloongson-mmi' will be > >> setted for Loongson-3A only. > > > >The pattern we've used for other CPUs is to build support for as many > >ISA extensions as possible, unless they are explicitly disabled. > >Distributions tend to want to set their own minimum ISA levels, and if > >they wanted to assert -mloongson-mmi they would already have added it > >to CFLAGS globally. > > > >Do you have any performance data for this change? > > > >If setting -mloongson-mmi means the compiler can do useful > >autovectorization, then that's probably true for other arches too (eg > >amd64 vs avx2), and we should support this kind of thing more > >generically. But as it stands I don't think this patch is a good idea. > > > First, that's introduce the history of '-march=loongson2f' and > '-mloongson-mmi'. > From loongson2f start, mmi is supported by loongson processor.
Yes. So that's why when we code, we should be very careful, especially when we work on base part of a OS, just like pixman. One, history mistake will make all of the people painful. An exmaple is about time_t on 32bit system. > Unfortunately, the compiler's support for MMI extention is not standardized. > Gcc compiler use '-march=loongson2f' for loongson2f at first, but from > Loongson-3A, > opcode of mmi instruction has changed, and '-march=loongson3a' is in replaced. That is the reason some of Loongson's extensions make upstream unhappy. You need be always very careful when you design a CPU. 如履薄冰. No zuo no die. > From last year, compile option for mmi instruction has been standardized. > Just like -mmsa for mips MSA. (MMI,LSX,LASX is Loongson SIMD extention.) > -mloongson-mmi for MMI (-march=loongson3a still works, but -mloongson-mmi > is recommended for new processors except Loongson2f. ) > -mloongson-sx for LSX > -mloongson-asx for LASX That is good news. > > Second, back to this patch itself. > I meet a problem when compile pixman on my Loongson3a with gcc, MMI can't be > enabled. > configure check failure: " linking mips:loongson_2f module with previous > mips:gs464 modules" > It can be solved by assign LS_CFLAGS="-mloongson-mmi" while config. > So I submit this patch in hope that no need to assign LS_CFLAGS explicitly. > This won't have much impact on performance as I know. Here is not about performance. You made a bad design, that is burden of history. > > Third, about the compatibility with Loongson2f. > This patch does not change the result of pixman compilation and running on > loongson2f. > Before add this patch, LS_CFLAGS will be setted as '-march=loongson2f' by > default, > After add this patch, LS_CFLAGS is still setted as '-march=loongson2f' if we > compile on the old environment. > It only makes MMI can be enabled without assign LS_CFLAGS explicitly while > compiling locally on loongson-3A. > That's why you need to guess from compiler. You can read the code of config.guess: http://git.savannah.gnu.org/gitweb/?p=config.git;a=blob;f=config.guess In fact I noticed that you have broken the build system of ffmpeg and some other project. Please STOP it. > > > _______________________________________________ > Pixman mailing list > [email protected] > https://lists.freedesktop.org/mailman/listinfo/pixman -- YunQiang Su _______________________________________________ Pixman mailing list [email protected] https://lists.freedesktop.org/mailman/listinfo/pixman
