Date: Sat, 22 Sep 2012 07:46:45 -0700 From: Steve Kargl <sgk@troutmask.apl.washington.edu> To: Konstantin Belousov <kostikbel@gmail.com> Cc: freebsd-current@freebsd.org, freebsd-toolchain@freebsd.org Subject: Re: More kernel performance tests on FreeBSD 10.0-CURRENT Message-ID: <20120922144645.GA10139@troutmask.apl.washington.edu> In-Reply-To: <20120922112014.GH37286@deviant.kiev.zoral.com.ua> References: <505CDE9C.3060504@andric.com> <20120922112014.GH37286@deviant.kiev.zoral.com.ua>
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On Sat, Sep 22, 2012 at 02:20:14PM +0300, Konstantin Belousov wrote: > On Fri, Sep 21, 2012 at 11:39:40PM +0200, Dimitry Andric wrote: > > Hi all, > > > > As a followup to my previous post about the performance of FreeBSD 10.0 > > kernels compiled with different compilers (clang and gcc), I did another > > series of tests, now on a more modern machine (Core i5-based). I also > > tested the performance with different compiler optimization settings. > > > > The attached text file[1] contains more information about these tests, > > performance data, and my conclusions. Any errors and omissions are also > > my fault, so if you notice them, please let me know. > > > > The executive summary: GENERIC kernels compiled with clang 3.2 are again > > a little faster than those compiled with gcc 4.2.1. For gcc, compiling > > with -O2 also gives a slightly faster kernel than with -O1, but for > > clang there is no measurable difference between those flags. > > > > Again, many thanks to Gavin Atkinson for providing the required > > hardware. > ... > > > Conclusion: > > ----------- > > Kernels compiled with clang are a little faster in real time for building world, > > and in system time the difference is even larger, roughly 10%. For clang, the > > difference between -O1 and -O2 is not measurable, but for gcc, -O2 is slightly > > faster than -O1. > > > > Thank you very much for finishing the initial assessment. > In my opinion, this positively closes the issue of the uncertainicity > of the performance impact of the proposed clang use by default for the > base system. It does not close everything. The kernel does not use floating point. I showed last week that clang may have problems with floating point. -- Steve
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