Commit 3491caf2 authored by Christian Borntraeger's avatar Christian Borntraeger Committed by Paolo Bonzini
Browse files

KVM: halt_polling: provide a way to qualify wakeups during poll 



Some wakeups should not be considered a sucessful poll. For example on
s390 I/O interrupts are usually floating, which means that _ALL_ CPUs
would be considered runnable - letting all vCPUs poll all the time for
transactional like workload, even if one vCPU would be enough.
This can result in huge CPU usage for large guests.
This patch lets architectures provide a way to qualify wakeups if they
should be considered a good/bad wakeups in regard to polls.

For s390 the implementation will fence of halt polling for anything but
known good, single vCPU events. The s390 implementation for floating
interrupts does a wakeup for one vCPU, but the interrupt will be delivered
by whatever CPU checks first for a pending interrupt. We prefer the
woken up CPU by marking the poll of this CPU as "good" poll.
This code will also mark several other wakeup reasons like IPI or
expired timers as "good". This will of course also mark some events as
not sucessful. As  KVM on z runs always as a 2nd level hypervisor,
we prefer to not poll, unless we are really sure, though.

This patch successfully limits the CPU usage for cases like uperf 1byte
transactional ping pong workload or wakeup heavy workload like OLTP
while still providing a proper speedup.

This also introduced a new vcpu stat "halt_poll_no_tuning" that marks
wakeups that are considered not good for polling.

Signed-off-by: default avatarChristian Borntraeger <borntraeger@de.ibm.com>
Acked-by: Radim Krčmář <rkrcmar@redhat.com> (for an earlier version)
Cc: David Matlack <dmatlack@google.com>
Cc: Wanpeng Li <kernellwp@gmail.com>
[Rename config symbol. - Paolo]
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent d7e1633a

arch/arm/include/asm/kvm_host.h

+2 −0
Original line number Diff line number Diff line
@@ -187,6 +187,7 @@ struct kvm_vm_stat { 
struct kvm_vcpu_stat {

	u32 halt_successful_poll;

	u32 halt_attempted_poll;

	u32 halt_poll_invalid;

	u32 halt_wakeup;

	u32 hvc_exit_stat;

	u64 wfe_exit_stat;
@@ -282,6 +283,7 @@ static inline void kvm_arch_hardware_unsetup(void) {} 
static inline void kvm_arch_sync_events(struct kvm *kvm) {}

static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {}

static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {}

static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {}



static inline void kvm_arm_init_debug(void) {}

static inline void kvm_arm_setup_debug(struct kvm_vcpu *vcpu) {}

arch/arm64/include/asm/kvm_host.h

+2 −0
Original line number Diff line number Diff line
@@ -293,6 +293,7 @@ struct kvm_vm_stat { 
struct kvm_vcpu_stat {

	u32 halt_successful_poll;

	u32 halt_attempted_poll;

	u32 halt_poll_invalid;

	u32 halt_wakeup;

	u32 hvc_exit_stat;

	u64 wfe_exit_stat;
@@ -357,6 +358,7 @@ static inline void kvm_arch_hardware_unsetup(void) {} 
static inline void kvm_arch_sync_events(struct kvm *kvm) {}

static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {}

static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {}

static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {}



void kvm_arm_init_debug(void);

void kvm_arm_setup_debug(struct kvm_vcpu *vcpu);

arch/mips/include/asm/kvm_host.h

+2 −0
Original line number Diff line number Diff line
@@ -122,6 +122,7 @@ struct kvm_vcpu_stat { 
	u32 flush_dcache_exits;

	u32 halt_successful_poll;

	u32 halt_attempted_poll;

	u32 halt_poll_invalid;

	u32 halt_wakeup;

};
@@ -812,5 +813,6 @@ static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {} 
static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {}

static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) {}

static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {}

static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {}



#endif /* __MIPS_KVM_HOST_H__ */

arch/mips/kvm/mips.c

+1 −0
Original line number Diff line number Diff line
@@ -56,6 +56,7 @@ struct kvm_stats_debugfs_item debugfs_entries[] = { 
	{ "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_poll_invalid", VCPU_STAT(halt_poll_invalid), KVM_STAT_VCPU },

	{ "halt_wakeup",  VCPU_STAT(halt_wakeup),	 KVM_STAT_VCPU },

	{NULL}

};

arch/powerpc/include/asm/kvm_host.h

+2 −0
Original line number Diff line number Diff line
@@ -116,6 +116,7 @@ struct kvm_vcpu_stat { 
	u32 ext_intr_exits;

	u32 halt_successful_poll;

	u32 halt_attempted_poll;

	u32 halt_poll_invalid;

	u32 halt_wakeup;

	u32 dbell_exits;

	u32 gdbell_exits;
@@ -727,5 +728,6 @@ static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {} 
static inline void kvm_arch_exit(void) {}

static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) {}

static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {}

static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {}



#endif /* __POWERPC_KVM_HOST_H__ */

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