Ganeti howto: add a section about how to change the CPU type

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

diff --git a/input/howto/install-ganeti.creole b/input/howto/install-ganeti.creole
index 3af7113..d18ef4b 100644 (file)
--- a/input/howto/install-ganeti.creole
+++ b/input/howto/install-ganeti.creole
@@ -467,3 +467,85 @@ Order is important, or else things get very, very confused and the world needs a
 {{{
   gnt-cluster command "echo 1 > /sys/bus/pci/devices/0000:0e:00.0/cciss0/rescan"
 }}}
+
+=== Change the CPU type ===
+
+Modern processors come with a wide variety of additional instruction sets (SSE, AES-NI, etc.) which vary from processor to processor, but can greatly improve the performance depending on the workload. Ganeti and QEMU default to a compatible subset of cpu features called qemu64, so that if the host processor is changed, or a live migration is performed, the guest will see its CPUfeatures unchanged. This is great for compatibility but comes at a performance cost.
+
+The CPU presented to the guests can easily be changed, using the cpu_type option in Ganeti hypervisor options. However to still be able to live-migrate VMs from one host to another, the CPU presented to the guest should be the common denominator of all hosts in the cluster. Otherwise a live migration between two different CPU types could crash the instance.
+
+For homogeneous clusters it is possible to use the host cpu type:
+
+{{{
+  gnt-cluster modify -H kvm:cpu_type='host'
+}}}
+
+Otherwise QEMU provides a set of generic CPU for each generation, that can be queried that way:
+
+{{{
+$ qemu-system-x86_64 -cpu ?
+
+x86           qemu64  QEMU Virtual CPU version 2.1.2
+x86           phenom  AMD Phenom(tm) 9550 Quad-Core Processor
+x86         core2duo  Intel(R) Core(TM)2 Duo CPU     T7700  @ 2.40GHz
+x86            kvm64  Common KVM processor
+x86           qemu32  QEMU Virtual CPU version 2.1.2
+x86            kvm32  Common 32-bit KVM processor
+x86          coreduo  Genuine Intel(R) CPU           T2600  @ 2.16GHz
+x86              486
+x86          pentium
+x86         pentium2
+x86         pentium3
+x86           athlon  QEMU Virtual CPU version 2.1.2
+x86             n270  Intel(R) Atom(TM) CPU N270   @ 1.60GHz
+x86           Conroe  Intel Celeron_4x0 (Conroe/Merom Class Core 2)
+x86           Penryn  Intel Core 2 Duo P9xxx (Penryn Class Core 2)
+x86          Nehalem  Intel Core i7 9xx (Nehalem Class Core i7)
+x86         Westmere  Westmere E56xx/L56xx/X56xx (Nehalem-C)
+x86      SandyBridge  Intel Xeon E312xx (Sandy Bridge)
+x86          Haswell  Intel Core Processor (Haswell)
+x86        Broadwell  Intel Core Processor (Broadwell)
+x86       Opteron_G1  AMD Opteron 240 (Gen 1 Class Opteron)
+x86       Opteron_G2  AMD Opteron 22xx (Gen 2 Class Opteron)
+x86       Opteron_G3  AMD Opteron 23xx (Gen 3 Class Opteron)
+x86       Opteron_G4  AMD Opteron 62xx class CPU
+x86       Opteron_G5  AMD Opteron 63xx class CPU
+x86             host  KVM processor with all supported host features (only available in KVM mode)
+
+Recognized CPUID flags:
+  pbe ia64 tm ht ss sse2 sse fxsr mmx acpi ds clflush pn pse36 pat cmov mca pge mtrr sep apic cx8 mce pae msr tsc pse de vme fpu
+  hypervisor rdrand f16c avx osxsave xsave aes tsc-deadline popcnt movbe x2apic sse4.2|sse4_2 sse4.1|sse4_1 dca pcid pdcm xtpr cx16 fma cid ssse3 tm2 est smx vmx ds_cpl monitor dtes64 pclmulqdq|pclmuldq pni|sse3
+  smap adx rdseed rtm invpcid erms bmi2 smep avx2 hle bmi1 fsgsbase
+  3dnow 3dnowext lm|i64 rdtscp pdpe1gb fxsr_opt|ffxsr mmxext nx|xd syscall
+  perfctr_nb perfctr_core topoext tbm nodeid_msr tce fma4 lwp wdt skinit xop ibs osvw 3dnowprefetch misalignsse sse4a abm cr8legacy extapic svm cmp_legacy lahf_lm
+  invtsc
+  pmm-en pmm phe-en phe ace2-en ace2 xcrypt-en xcrypt xstore-en xstore
+  kvmclock-stable-bit kvm_pv_unhalt kvm_pv_eoi kvm_steal_time kvm_asyncpf kvmclock kvm_mmu kvm_nopiodelay kvmclock
+  pfthreshold pause_filter decodeassists flushbyasid vmcb_clean tsc_scale nrip_save svm_lock lbrv npt
+}}}
+
+For example on a cluster using both Sandy Bridge and Haswell CPU, the following command can be used:
+{{{
+  gnt-cluster modify -H kvm:cpu_type='SandyBridge'
+}}}
+
+Here is a typical improvement one can get on the AES openssl benchmarks.
+
+With the default qemu64 CPU type:
+{{{
+  type             16 bytes     64 bytes    256 bytes   1024 bytes   8192 bytes
+  aes-128-cbc     175481.21k   195151.55k   199307.09k   201209.51k   201359.36k
+  aes-128-gcm      49971.64k    57688.17k   135092.14k   144172.37k   146511.19k
+  aes-256-cbc     130209.34k   141268.76k   142547.54k   144185.00k   144777.22k
+  aes-256-gcm      39249.19k    44492.61k   114492.76k   123000.83k   125501.44k
+
+}}}
+
+With the SandyBridge CPU type:
+{{{
+  type             16 bytes     64 bytes    256 bytes   1024 bytes   8192 bytes
+  aes-128-cbc     376040.16k   477377.32k   484083.37k   391323.31k   389589.67k
+  aes-128-gcm     215921.26k   592407.87k   777246.21k   836795.39k   835971.75k
+  aes-256-cbc     309840.39k   328612.18k   330784.68k   324245.16k   328116.91k
+  aes-256-gcm     160820.14k   424322.20k   557212.50k   599435.61k   610459.65k
+}}}