Commit 0fd7e098 authored by Liang Li's avatar Liang Li Committed by Paolo Bonzini
Browse files

kvmclock: add a new function to update env->tsc. 



The commit 317b0a6d fixed an issue which caused by the outdated
env->tsc value, but the fix lead to 'cpu_synchronize_all_states()'
called twice during live migration. The 'cpu_synchronize_all_states()'
takes about 130us for a VM which has 4 vcpus, it's a bit expensive.

Synchronize the whole CPU context just for updating env->tsc is too
wasting, this patch use a new function to update the env->tsc.
Comparing to 'cpu_synchronize_all_states()', it only takes about 20us.

Signed-off-by: default avatarLiang Li <liang.z.li@intel.com>
Message-Id: <1446695464-27116-2-git-send-email-liang.z.li@intel.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent b553a042

hw/i386/kvm/clock.c

+2 −16
Original line number Diff line number Diff line
@@ -17,7 +17,7 @@ 
#include "qemu/host-utils.h"

#include "sysemu/sysemu.h"

#include "sysemu/kvm.h"

#include "sysemu/cpus.h"

#include "kvm_i386.h"

#include "hw/sysbus.h"

#include "hw/kvm/clock.h"
@@ -125,21 +125,7 @@ static void kvmclock_vm_state_change(void *opaque, int running, 
            return;

        }



        cpu_synchronize_all_states();

        /* In theory, the cpu_synchronize_all_states() call above wouldn't

         * affect the rest of the code, as the VCPU state inside CPUState

         * is supposed to always match the VCPU state on the kernel side.

         *

         * In practice, calling cpu_synchronize_state() too soon will load the

         * kernel-side APIC state into X86CPU.apic_state too early, APIC state

         * won't be reloaded later because CPUState.vcpu_dirty==true, and

         * outdated APIC state may be migrated to another host.

         *

         * The real fix would be to make sure outdated APIC state is read

         * from the kernel again when necessary. While this is not fixed, we

         * need the cpu_clean_all_dirty() call below.

         */

        cpu_clean_all_dirty();

        kvm_synchronize_all_tsc();



        ret = kvm_vm_ioctl(kvm_state, KVM_GET_CLOCK, &data);

        if (ret < 0) {

target-i386/kvm.c

+45 −0
Original line number Diff line number Diff line
@@ -111,6 +111,51 @@ bool kvm_allows_irq0_override(void) 
    return !kvm_irqchip_in_kernel() || kvm_has_gsi_routing();

}



static int kvm_get_tsc(CPUState *cs)

{

    X86CPU *cpu = X86_CPU(cs);

    CPUX86State *env = &cpu->env;

    struct {

        struct kvm_msrs info;

        struct kvm_msr_entry entries[1];

    } msr_data;

    int ret;



    if (env->tsc_valid) {

        return 0;

    }



    msr_data.info.nmsrs = 1;

    msr_data.entries[0].index = MSR_IA32_TSC;

    env->tsc_valid = !runstate_is_running();



    ret = kvm_vcpu_ioctl(CPU(cpu), KVM_GET_MSRS, &msr_data);

    if (ret < 0) {

        return ret;

    }



    env->tsc = msr_data.entries[0].data;

    return 0;

}



static inline void do_kvm_synchronize_tsc(void *arg)

{

    CPUState *cpu = arg;



    kvm_get_tsc(cpu);

}



void kvm_synchronize_all_tsc(void)

{

    CPUState *cpu;



    if (kvm_enabled()) {

        CPU_FOREACH(cpu) {

            run_on_cpu(cpu, do_kvm_synchronize_tsc, cpu);

        }

    }

}



static struct kvm_cpuid2 *try_get_cpuid(KVMState *s, int max)

{

    struct kvm_cpuid2 *cpuid;

target-i386/kvm_i386.h

+1 −0
Original line number Diff line number Diff line
@@ -15,6 +15,7 @@ 


bool kvm_allows_irq0_override(void);

bool kvm_has_smm(void);

void kvm_synchronize_all_tsc(void);

void kvm_arch_reset_vcpu(X86CPU *cs);

void kvm_arch_do_init_vcpu(X86CPU *cs);