[Qemu-devel] [PATCH v4 0/2] target-i386: save/restore vcpu's TSC rate during migration

[Haozhong Zhang]

This patchset enables QEMU to save/restore vcpu's TSC rate during the
migration on machine types pc-*-2.5 or newer.

On the source machine:
 * If the vcpu's TSC rate is specified by the cpu option 'tsc-freq',
   then this user-specified TSC rate will be migrated.
 * Otherwise, the TSC rate returned by KVM_GET_TSC_KHZ will be
   migrated. For a fresh VM, this is the host TSC rate.

On the destination machine:
 * If the vcpu's TSC rate has been specified by the cpu option
   'tsc-freq' and is inconsistent with the migrated TSC rate, then
   the migration will be aborted.
 * Otherwise, QEMU will try to use the migrated TSC rate. If KVM on
   the destination supports TSC scaling, guest programs will observe a
   consistent TSC rate across the migration. If TSC scaling is not
   supported, the migration will not be aborted and QEMU will behave
   like before, i.e using the host TSC rate instead.

Changes in v4:
 * Make all code x86 specific.
 * Abort the migration if the user-specified TSC rate is inconsistent
   with the migrated TSC rate.
 * Move the sanity check to cpu_post_load().
 * All KVM_SET_TSC_KHZ and save/restore use env->tsc_khz.
 * Replace env->tsc_khz_saved with env->user_tsc_khz, and only use the
   latter for sanity check.

Changes in v3:
 * Change the cpu option 'save-tsc-freq' to an internal flag.
 * Remove the cpu option 'load-tsc-freq' and change the logic of
   loading the migrated TSC rate as above.
 * Move the setup of migrated TSC rate back to
   do_kvm_cpu_synchronize_post_init().

Changes in v2:
 * Add a pair of cpu options 'save-tsc-freq' and 'load-tsc-freq' to
   control the migration of vcpu's TSC rate.
 * Move all logic of setting TSC rate to target-i386.
 * Remove the duplicated TSC setup in kvm_arch_init_vcpu().

Haozhong Zhang (2):
  target-i386: fallback vcpu's TSC rate to value returned by KVM
  target-i386: add support to migrate vcpu's TSC rate

 hw/i386/pc.c          |  1 +
 hw/i386/pc_piix.c     |  1 +
 hw/i386/pc_q35.c      |  1 +
 include/hw/i386/pc.h  |  1 +
 target-i386/cpu.c     |  2 +-
 target-i386/cpu.h     |  1 +
 target-i386/kvm.c     | 47 +++++++++++++++++++++++++++++++++++++++++++++++
 target-i386/machine.c | 28 ++++++++++++++++++++++++++++
 8 files changed, 81 insertions(+), 1 deletion(-)

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2.6.3