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Path: ...!weretis.net!feeder9.news.weretis.net!news.nk.ca!rocksolid2!i2pn2.org!.POSTED!not-for-mail From: mitchalsup@aol.com (MitchAlsup1) Newsgroups: comp.arch Subject: Re: Continuations Date: Wed, 17 Jul 2024 19:22:52 +0000 Organization: Rocksolid Light Message-ID: <ef12aa647464a3ebe3bd208c13a3c40c@www.novabbs.org> References: <v6tbki$3g9rg$1@dont-email.me> <47689j5gbdg2runh3t7oq2thodmfkalno6@4ax.com> <v71vqu$gomv$9@dont-email.me> <116d9j5651mtjmq4bkjaheuf0pgpu6p0m8@4ax.com> <f8c6c5b5863ecfc1ad45bb415f0d2b49@www.novabbs.org> <7u7e9j5dthm94vb2vdsugngjf1cafhu2i4@4ax.com> <0f7b4deb1761f4c485d1dc3b21eb7cb3@www.novabbs.org> <v78soj$1tn73$1@dont-email.me> <4bbc6af7baab612635eef0de4847ba5b@www.novabbs.org> <v792kn$1v70t$1@dont-email.me> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Injection-Info: i2pn2.org; logging-data="3631347"; mail-complaints-to="usenet@i2pn2.org"; posting-account="65wTazMNTleAJDh/pRqmKE7ADni/0wesT78+pyiDW8A"; User-Agent: Rocksolid Light X-Spam-Checker-Version: SpamAssassin 4.0.0 X-Rslight-Site: $2y$10$gyIFnW.fM6YBOD5CmcabV.uzEQ3OLGDdtdGWQfwByqRJ5fUf90RFu X-Rslight-Posting-User: ac58ceb75ea22753186dae54d967fed894c3dce8 Bytes: 3369 Lines: 53 On Wed, 17 Jul 2024 18:30:47 +0000, Stephen Fuld wrote: > MitchAlsup1 wrote: > >> On Wed, 17 Jul 2024 16:50:27 +0000, Thomas Koenig wrote: >> >>>MitchAlsup1 <mitchalsup@aol.com> schrieb: >>> >>> > What I am talking about is to improve their performance until a >>> > sin() takes about the same number of cycles of FDIV, not 10× more. >>> >>> Maybe time for a little story. >>> >>> Some unspecified time ago, a colleague did CFD calculations which >>> included fluid flow (including turbulence modelling and diffusion) >>> and quite a few chemical reactions together. So, he evaluated a >>> huge number of Arrhenius equations, >>> >>> k = A * exp(-E_a/(R*T)) >>> >>> and because some of the reactions he looked at were highly >>> exothermic or endothermic, he needed tiny relaxation factors (aka >>> small steps). His calculaiton spent most of the time evaluating >>> the Arrhenius equation above many, many, many, many times. >>> >>> A single calculation took months, and he didn't use weak hardware. >>> >>> A fully pipelined evaluation of, let's say, four parallel exp and >>> four parallel fdiv instructions would have reduced his calculation >>> time by orders of magnitude, and allowed him to explore the design >>> space instead of just scratching the surface. >>> >>> (By the way, if I had found a reasonable way to incorporate the >>> Arrhenius equation into your ISA, I would have done so already :-) >> >> FMUL Rt,RR,RT >> FDIV Rt,-RE,Rt >> EXP Rt,Rt >> FMUL Rk,RA,Rt >> >> Does not look "all that bad" to me. > > So for your GbOoO CPU, how many of the various FP operations, and the > EXP instruction can be done in parallel? FMUL is 4 cycles of latency fully pipelined FDIV is ~20 cycles of latency not pipelined EXP is ~16 cycles of latency not pipelined They are all performed in the FMAC unit and here the instructions are serially dependent. So, 44 cycles of latency, a 1-wide machine and a 6-wide machine would see the same latency; that is, GBOoO is not a differentiator.