[MLton] -mtune=opteron considered harmful
fluet at tti-c.org
Mon Aug 13 16:33:07 PDT 2007
On Mon, 13 Aug 2007, Matthew Fluet wrote:
> On Tue, 14 Aug 2007, Florian Weimer wrote:
>> On Debian unstable at least, the C parts of MLton are compiled with
>> -mtune=opteron. With recent GCCs (4.1 in some distros, and 4.2
>> mainline), this overrides the default of -mtune=generic, and produces
>> code that doesn't run very well on Netburst machines. (The impact on
>> the Core architecture should be less significant, if measurable at
> Fair enough; I'm not sure it was doing anything particularly useful.
By which, I mean that (by default) it is only used when compiling the
runtime. (It would also be used when compiling the programs with the
C-codegen, but GCC 4.1.2 and 4.2.1 have bugs that cause gcc ICEs with the
C-codegen code.) So, the differences in tuning are mainly affecting the
garbage collector. I wouldn't expect the difference to be measurable on
any machine, except for programs that are spending a significant portion
of their time in the garbage collector.
Do you have a program/machine pair that is measurably faster without
-mtune=opteron, or is this just an anecdotal recommendation?
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