From: Steven Noonan Date: Mon, 17 Aug 2009 21:43:55 GMT Subject: Re: Linus' sha1 is much faster! Message-ID: In-Reply-To: On Mon, Aug 17, 2009 at 9:22 AM, Linus Torvalds wrote: > > > On Mon, 17 Aug 2009, Steven Noonan wrote: >> >> Interesting. I compared Linus' implementation to the public domain one >> by Steve Reid[1] > > You _really_ need to talk about what kind of environment you have. > > There are three major issues: >  - Netburst vs non-netburst >  - 32-bit vs 64-bit >  - compiler version Right. I'm running a Core 2 "Merom" 2.33GHz. The code was compiled for x86_64 with GCC 4.2.1. I didn't _expect_ it to compile for x86_64, but apparently the version of GCC that ships with Xcode 3.2 defaults to compiling 64-bit code on machines that are capable of running it. > > Steve Reid's code looks great, but the way it is coded, gcc makes a mess > of it, which is exactly what my SHA1 tries to avoid. > > [ In contrast, gcc does very well on just about _any_ straightforward >  unrolled SHA1 C code if the target architecture is something like PPC or >  ia64 that has enough registers to keep it all in registers. > >  I haven't really tested other compilers - a less aggressive compiler >  would actually do _better_ on SHA1, because the problem with gcc is that >  it turns the whole temporary 16-entry word array into register accesses, >  and tries to do register allocation on that _array_. > >  That is wonderful for the above-mentioned PPC and IA64, but it makes gcc >  create totally crazy code when there aren't enough registers, and then >  gcc starts spilling randomly (ie it starts spilling a-e etc). This is >  why the compiler and version matters so much. ] > >> (average of 5 runs) >> Linus' sha1: 283MB/s >> Steve Reid's sha1: 305MB/s > > So I get very different results: > >        #             TIME[s] SPEED[MB/s] >        Reid            2.742       222.6 >        linus           1.464         417 Added -m32: Steve Reid: 156MB/s Linus: 209MB/s So on x86, your code really kicks butt. > this is Intel Nehalem, but compiled for 32-bit mode (which is the more > challenging one because x86-32 only has 7 general-purpose registers), and > with gcc-4.4.0. > >                        Linus >