What are differences between linux kernel compiled for generic x86/64 vs Xeon or others -


in linux kernel config there option change cpu family, precompiled kernels generic x86/64.

i have xeon e3 cpu wondering happen if pick core duo/newer xeon there.

what differences here? there point in compiling kernel cpu family, instead of generic one? kernel optimized xeon work on non-xeon cpu's? did ever measured differences in performance , on?

it select corresponding config option (from arch/x86/kconfig.cpu):

config mcore2      bool "core 2/newer xeon"

generally speaking, config_mcore2 enable compiler option -mtune=core2 on 32-bit builds , -march=core2 (it can found in makefiles arch/x86/makefile , arch/x86/makefile_32.cpu).

these options described in gcc manual page:

-march=cpu-type

generate instructions machine type cpu-type. in contrast -mtune=cpu-type, merely tunes generated code specified cpu-type, -march=cpu-type allows gcc generate code may not run @ on processors other 1 indicated.

specifying -march=cpu-type implies -mtune=cpu-type.

core2

intel core 2 cpu 64-bit extensions, mmx, sse, sse2, sse3 , ssse3 instruction set support.

speaking on overall effect of compile option application performance, should relatively low:

  • in kernel overall architecture matters. i.e. contending lock may kill performance , lock-free data-structure gain it. , work regardless of compiler options.
  • there small number operations in kernel require simd operations enabled optimization (except copying arrays or strings probably). there small number of cpu-intensive operations in kernel @ all. optimizations cacheline size may work well.
  • for applications not kernel-bound spend of time in userspace, calling kernel using system calls effect of optimization reduced proportionally. i.e. 2% kernel performance improvement app spends 10% in kernel, you'll 0.2% overall performance increase.

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