On Tuesday 09 April 2013 12:31:44 PM IST, Pandu Poluan wrote:
On Apr 9, 2013 1:16 PM, "Michael Hampicke" <gentoo-u...@hadt.biz <mailto:gentoo-u...@hadt.biz>> wrote: > > Am 09.04.2013 05:50, schrieb Nilesh Govindrajan: > > I have two Gentoo VMs at Hetzner and the CPU supports 64 bit (grep lm > > /proc/cpuinfo = true). > > > > But something funny, gcc -march=native -mtune=native -v -E - 2>&1 > > </dev/null returns this: > > > > Using built-in specs. > > COLLECT_GCC=/usr/x86_64-pc-linux-gnu/gcc-bin/4.6.3/gcc > > COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-pc-linux-gnu/4.6.3/lto-wrapper > > Target: x86_64-pc-linux-gnu > > Configured with: > > /var/tmp/portage/sys-devel/gcc-4.6.3/work/gcc-4.6.3/configure > > --prefix=/usr --bindir=/usr/x86_64-pc-linux-gnu/gcc-bin/4.6.3 > > --includedir=/usr/lib/gcc/x86_64-pc-linux-gnu/4.6.3/include > > --datadir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.6.3 > > --mandir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.6.3/man > > --infodir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.6.3/info > > --with-gxx-include-dir=/usr/lib/gcc/x86_64-pc-linux-gnu/4.6.3/include/g++-v4 > > --host=x86_64-pc-linux-gnu --build=x86_64-pc-linux-gnu --disable-altivec > > --disable-fixed-point --without-ppl --without-cloog --enable-lto > > --enable-nls --without-included-gettext --with-system-zlib > > --enable-obsolete --disable-werror --enable-secureplt --enable-multilib > > --enable-libmudflap --disable-libssp --enable-libgomp > > --with-python-dir=/share/gcc-data/x86_64-pc-linux-gnu/4.6.3/python > > --enable-checking=release --disable-libgcj --enable-libstdcxx-time > > --enable-languages=c,c++,fortran --enable-shared --enable-threads=posix > > --enable-__cxa_atexit --enable-clocale=gnu --enable-targets=all > > --with-bugurl=http://bugs.gentoo.org/ --with-pkgversion='Gentoo 4.6.3 > > p1.11, pie-0.5.2' > > Thread model: posix > > gcc version 4.6.3 (Gentoo 4.6.3 p1.11, pie-0.5.2) > > COLLECT_GCC_OPTIONS='-march=native' '-mtune=native' '-v' '-E' > > /usr/libexec/gcc/x86_64-pc-linux-gnu/4.6.3/cc1 -E -quiet -v - > > -march=pentium-m -mcx16 -msahf -mno-movbe -mno-aes -mno-pclmul -mpopcnt > > -mno-abm -mno-lwp -mno-fma -mno-fma4 -mno-xop -mbmi -mno-tbm -mno-avx > > -mno-sse4.2 -mno-sse4.1 --param l1-cache-size=32 --param > > l1-cache-line-size=64 --param l2-cache-size=4096 -mtune=generic > > ignoring nonexistent directory "/usr/local/include" > > ignoring nonexistent directory > > "/usr/lib/gcc/x86_64-pc-linux-gnu/4.6.3/../../../../x86_64-pc-linux-gnu/include" > > > > #include "..." search starts here: > > #include <...> search starts here: > > /usr/lib/gcc/x86_64-pc-linux-gnu/4.6.3/include > > /usr/lib/gcc/x86_64-pc-linux-gnu/4.6.3/include-fixed > > /usr/include > > End of search list. > > # 1 "<stdin>" > > <stdin>:1:0: error: CPU you selected does not support x86-64 instruction > > set > > > > It is returning pentium-m as architecture, which indeed is 32bit. I'm > > presently running the VM with -march=core2, but this is very weird. > > > > This is the /proc/cpuinfo: > > > > processor : 0 > > vendor_id : GenuineIntel > > cpu family : 6 > > model : 2 > > model name : QEMU Virtual CPU version 1.0 > > stepping : 3 > > microcode : 0x1 > > cpu MHz : 3399.998 > > cache size : 4096 KB > > fpu : yes > > fpu_exception : yes > > cpuid level : 4 > > wp : yes > > flags : fpu de pse tsc msr pae mce cx8 apic sep mtrr pge mca > > cmov pse36 clflush mmx fxsr sse sse2 syscall nx lm rep_good nopl pni vmx > > cx16 popcnt hypervisor lahf_lm > > bogomips : 6799.99 > > clflush size : 64 > > cache_alignment : 64 > > address sizes : 40 bits physical, 48 bits virtual > > power management: > > > > Any idea what should be the march/mtune value? > > > > I don't have any experience with Hetzner's VMs - I only use their > dedicated machines :) > > But as a more generic tip, you should install gentoo in VMs only with > generic optimization. You can not safely rely on what CPU your VM will > get. Maybe in 6 months the host your vm is on crashes, and your vm will > be migrated to a new system with totally different cpu (actual hardware > cpu or the cpu configuration that qemu is going to emulate). > One tip for me: If your VMs are 64-bit, obviously the underlying CPU must be 64-bit. So, setting -march=nocona should be safe (Nocona is Intel's first AMD64-compatible CPU). Rgds, --
Well, it's a KVM virtual machine. And I'm *currently running* it with -march=core2 on 64bit, but that isn't very safe because it may be migrated any time in case the host fails. I guess it would be best to use generic x86_64? Or perhaps switch to 32bit because it's just 2 GB of RAM and it can't be bumped up any further (top end config).
Some search reveals that it's an upstream bug where the CPU is detected as pentium m which happens to be 32 bit.
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