Am 09.04.2013 14:53, schrieb Nilesh Govindrajan: > 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. >
I use this on 64bit VMs, but maybe nocona is better? CHOST=""x86_64-pc-linux-gnu"" CFLAGS="-march=k8 -O2 -pipe"
