Re: [PATCH] KVM: add halt_attempted_poll to VCPU stats

From: David Matlack
Date: Tue Sep 15 2015 - 13:21:51 EST

On Tue, Sep 15, 2015 at 9:27 AM, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
> This new statistic can help diagnosing VCPUs that, for any reason,
> trigger bad behavior of halt_poll_ns autotuning.
>
> For example, say halt_poll_ns = 480000, and wakeups are spaced exactly
> like 479us, 481us, 479us, 481us. Then KVM always fails polling and wastes
> 10+20+40+80+160+320+480 = 1110 microseconds out of every
> 479+481+479+481+479+481+479 = 3359 microseconds. The VCPU then
> is consuming about 30% more CPU than it would use without
> polling. This would show as an abnormally high number of
> attempted polling compared to the successful polls.

Reviewed-by: David Matlack <dmatlack@xxxxxxxxxx>

>
> Cc: Christian Borntraeger <borntraeger@xxxxxxxxxx<
> Cc: David Matlack <dmatlack@xxxxxxxxxx>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
> arch/arm/include/asm/kvm_host.h | 1 +
> arch/arm64/include/asm/kvm_host.h | 1 +
> arch/mips/include/asm/kvm_host.h | 1 +
> arch/mips/kvm/mips.c | 1 +
> arch/powerpc/include/asm/kvm_host.h | 1 +
> arch/powerpc/kvm/book3s.c | 1 +
> arch/powerpc/kvm/booke.c | 1 +
> arch/s390/include/asm/kvm_host.h | 1 +
> arch/s390/kvm/kvm-s390.c | 1 +
> arch/x86/include/asm/kvm_host.h | 1 +
> arch/x86/kvm/x86.c | 1 +
> virt/kvm/kvm_main.c | 1 +
> 12 files changed, 12 insertions(+)
>
> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
> index dcba0fa5176e..687ddeba3611 100644
> --- a/arch/arm/include/asm/kvm_host.h
> +++ b/arch/arm/include/asm/kvm_host.h
> @@ -148,6 +148,7 @@ struct kvm_vm_stat {
>
> struct kvm_vcpu_stat {
> u32 halt_successful_poll;
> + u32 halt_attempted_poll;
> u32 halt_wakeup;
> };
>
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 415938dc45cf..486594583cc6 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -195,6 +195,7 @@ struct kvm_vm_stat {
>
> struct kvm_vcpu_stat {
> u32 halt_successful_poll;
> + u32 halt_attempted_poll;
> u32 halt_wakeup;
> };
>
> diff --git a/arch/mips/include/asm/kvm_host.h b/arch/mips/include/asm/kvm_host.h
> index e8c8d9d0c45f..3a54dbca9f7e 100644
> --- a/arch/mips/include/asm/kvm_host.h
> +++ b/arch/mips/include/asm/kvm_host.h
> @@ -128,6 +128,7 @@ struct kvm_vcpu_stat {
> u32 msa_disabled_exits;
> u32 flush_dcache_exits;
> u32 halt_successful_poll;
> + u32 halt_attempted_poll;
> u32 halt_wakeup;
> };
>
> diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
> index cd4c129ce743..49ff3bfc007e 100644
> --- a/arch/mips/kvm/mips.c
> +++ b/arch/mips/kvm/mips.c
> @@ -55,6 +55,7 @@ struct kvm_stats_debugfs_item debugfs_entries[] = {
> { "msa_disabled", VCPU_STAT(msa_disabled_exits), KVM_STAT_VCPU },
> { "flush_dcache", VCPU_STAT(flush_dcache_exits), KVM_STAT_VCPU },
> { "halt_successful_poll", VCPU_STAT(halt_successful_poll), KVM_STAT_VCPU },
> + { "halt_attempted_poll", VCPU_STAT(halt_attempted_poll), KVM_STAT_VCPU },
> { "halt_wakeup", VCPU_STAT(halt_wakeup), KVM_STAT_VCPU },
> {NULL}
> };
> diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
> index 98eebbf66340..195886a583ba 100644
> --- a/arch/powerpc/include/asm/kvm_host.h
> +++ b/arch/powerpc/include/asm/kvm_host.h
> @@ -108,6 +108,7 @@ struct kvm_vcpu_stat {
> u32 dec_exits;
> u32 ext_intr_exits;
> u32 halt_successful_poll;
> + u32 halt_attempted_poll;
> u32 halt_wakeup;
> u32 dbell_exits;
> u32 gdbell_exits;
> diff --git a/arch/powerpc/kvm/book3s.c b/arch/powerpc/kvm/book3s.c
> index d75bf325f54a..cf009167d208 100644
> --- a/arch/powerpc/kvm/book3s.c
> +++ b/arch/powerpc/kvm/book3s.c
> @@ -53,6 +53,7 @@ struct kvm_stats_debugfs_item debugfs_entries[] = {
> { "ext_intr", VCPU_STAT(ext_intr_exits) },
> { "queue_intr", VCPU_STAT(queue_intr) },
> { "halt_successful_poll", VCPU_STAT(halt_successful_poll), },
> + { "halt_attempted_poll", VCPU_STAT(halt_attempted_poll), },
> { "halt_wakeup", VCPU_STAT(halt_wakeup) },
> { "pf_storage", VCPU_STAT(pf_storage) },
> { "sp_storage", VCPU_STAT(sp_storage) },
> diff --git a/arch/powerpc/kvm/booke.c b/arch/powerpc/kvm/booke.c
> index ae458f0fd061..fd5875179e5c 100644
> --- a/arch/powerpc/kvm/booke.c
> +++ b/arch/powerpc/kvm/booke.c
> @@ -63,6 +63,7 @@ struct kvm_stats_debugfs_item debugfs_entries[] = {
> { "dec", VCPU_STAT(dec_exits) },
> { "ext_intr", VCPU_STAT(ext_intr_exits) },
> { "halt_successful_poll", VCPU_STAT(halt_successful_poll) },
> + { "halt_attempted_poll", VCPU_STAT(halt_attempted_poll) },
> { "halt_wakeup", VCPU_STAT(halt_wakeup) },
> { "doorbell", VCPU_STAT(dbell_exits) },
> { "guest doorbell", VCPU_STAT(gdbell_exits) },
> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
> index 3d012e071647..6ce4a0b7e8da 100644
> --- a/arch/s390/include/asm/kvm_host.h
> +++ b/arch/s390/include/asm/kvm_host.h
> @@ -210,6 +210,7 @@ struct kvm_vcpu_stat {
> u32 exit_validity;
> u32 exit_instruction;
> u32 halt_successful_poll;
> + u32 halt_attempted_poll;
> u32 halt_wakeup;
> u32 instruction_lctl;
> u32 instruction_lctlg;
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index c91eb941b444..2f807ab1725e 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -63,6 +63,7 @@ struct kvm_stats_debugfs_item debugfs_entries[] = {
> { "exit_program_interruption", VCPU_STAT(exit_program_interruption) },
> { "exit_instr_and_program_int", VCPU_STAT(exit_instr_and_program) },
> { "halt_successful_poll", VCPU_STAT(halt_successful_poll) },
> + { "halt_attempted_poll", VCPU_STAT(halt_attempted_poll) },
> { "halt_wakeup", VCPU_STAT(halt_wakeup) },
> { "instruction_lctlg", VCPU_STAT(instruction_lctlg) },
> { "instruction_lctl", VCPU_STAT(instruction_lctl) },
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 09acaa64ef8e..5bca6ac91e7c 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -718,6 +718,7 @@ struct kvm_vcpu_stat {
> u32 nmi_window_exits;
> u32 halt_exits;
> u32 halt_successful_poll;
> + u32 halt_attempted_poll;
> u32 halt_wakeup;
> u32 request_irq_exits;
> u32 irq_exits;
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 18d59b584dee..96e748c46bee 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -149,6 +149,7 @@ struct kvm_stats_debugfs_item debugfs_entries[] = {
> { "nmi_window", VCPU_STAT(nmi_window_exits) },
> { "halt_exits", VCPU_STAT(halt_exits) },
> { "halt_successful_poll", VCPU_STAT(halt_successful_poll) },
> + { "halt_attempted_poll", VCPU_STAT(halt_attempted_poll) },
> { "halt_wakeup", VCPU_STAT(halt_wakeup) },
> { "hypercalls", VCPU_STAT(hypercalls) },
> { "request_irq", VCPU_STAT(request_irq_exits) },
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 0b48aadedcee..c5de4ba9b33e 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2004,6 +2004,7 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
> if (vcpu->halt_poll_ns) {
> ktime_t stop = ktime_add_ns(ktime_get(), vcpu->halt_poll_ns);
>
> + ++vcpu->stat.halt_attempted_poll;
> do {
> /*
> * This sets KVM_REQ_UNHALT if an interrupt
> --
> 1.8.3.1
>
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