Re: [PATCH v1 1/4] KVM: stats: Support linear and logarithmic histogram statistics

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On Tue, Jul 06, 2021 at 06:03:47PM +0000, Jing Zhang wrote:
> Add new types of KVM stats, linear and logarithmic histogram.
> Histogram are very useful for observing the value distribution
> of time or size related stats.
> 
> Signed-off-by: Jing Zhang <jingzhangos@xxxxxxxxxx>
> ---
>  arch/arm64/kvm/guest.c    |  4 ---
>  arch/mips/kvm/mips.c      |  4 ---
>  arch/powerpc/kvm/book3s.c |  4 ---
>  arch/powerpc/kvm/booke.c  |  4 ---
>  arch/s390/kvm/kvm-s390.c  |  4 ---
>  arch/x86/kvm/x86.c        |  4 ---
>  include/linux/kvm_host.h  | 53 ++++++++++++++++++++++++++++-----------
>  include/linux/kvm_types.h | 16 ++++++++++++
>  include/uapi/linux/kvm.h  | 11 +++++---
>  virt/kvm/binary_stats.c   | 36 ++++++++++++++++++++++++++
>  10 files changed, 98 insertions(+), 42 deletions(-)
> 
> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
> index 1512a8007a78..cb44d8756fa7 100644
> --- a/arch/arm64/kvm/guest.c
> +++ b/arch/arm64/kvm/guest.c
> @@ -31,8 +31,6 @@
>  const struct _kvm_stats_desc kvm_vm_stats_desc[] = {
>  	KVM_GENERIC_VM_STATS()
>  };
> -static_assert(ARRAY_SIZE(kvm_vm_stats_desc) ==
> -		sizeof(struct kvm_vm_stat) / sizeof(u64));
>  
>  const struct kvm_stats_header kvm_vm_stats_header = {
>  	.name_size = KVM_STATS_NAME_SIZE,
> @@ -52,8 +50,6 @@ const struct _kvm_stats_desc kvm_vcpu_stats_desc[] = {
>  	STATS_DESC_COUNTER(VCPU, mmio_exit_kernel),
>  	STATS_DESC_COUNTER(VCPU, exits)
>  };
> -static_assert(ARRAY_SIZE(kvm_vcpu_stats_desc) ==
> -		sizeof(struct kvm_vcpu_stat) / sizeof(u64));
>  
>  const struct kvm_stats_header kvm_vcpu_stats_header = {
>  	.name_size = KVM_STATS_NAME_SIZE,
> diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
> index af9dd029a4e1..75c6f264c626 100644
> --- a/arch/mips/kvm/mips.c
> +++ b/arch/mips/kvm/mips.c
> @@ -41,8 +41,6 @@
>  const struct _kvm_stats_desc kvm_vm_stats_desc[] = {
>  	KVM_GENERIC_VM_STATS()
>  };
> -static_assert(ARRAY_SIZE(kvm_vm_stats_desc) ==
> -		sizeof(struct kvm_vm_stat) / sizeof(u64));
>  
>  const struct kvm_stats_header kvm_vm_stats_header = {
>  	.name_size = KVM_STATS_NAME_SIZE,
> @@ -85,8 +83,6 @@ const struct _kvm_stats_desc kvm_vcpu_stats_desc[] = {
>  	STATS_DESC_COUNTER(VCPU, vz_cpucfg_exits),
>  #endif
>  };
> -static_assert(ARRAY_SIZE(kvm_vcpu_stats_desc) ==
> -		sizeof(struct kvm_vcpu_stat) / sizeof(u64));
>  
>  const struct kvm_stats_header kvm_vcpu_stats_header = {
>  	.name_size = KVM_STATS_NAME_SIZE,
> diff --git a/arch/powerpc/kvm/book3s.c b/arch/powerpc/kvm/book3s.c
> index 79833f78d1da..5cc6e90095b0 100644
> --- a/arch/powerpc/kvm/book3s.c
> +++ b/arch/powerpc/kvm/book3s.c
> @@ -43,8 +43,6 @@ const struct _kvm_stats_desc kvm_vm_stats_desc[] = {
>  	STATS_DESC_ICOUNTER(VM, num_2M_pages),
>  	STATS_DESC_ICOUNTER(VM, num_1G_pages)
>  };
> -static_assert(ARRAY_SIZE(kvm_vm_stats_desc) ==
> -		sizeof(struct kvm_vm_stat) / sizeof(u64));
>  
>  const struct kvm_stats_header kvm_vm_stats_header = {
>  	.name_size = KVM_STATS_NAME_SIZE,
> @@ -88,8 +86,6 @@ const struct _kvm_stats_desc kvm_vcpu_stats_desc[] = {
>  	STATS_DESC_COUNTER(VCPU, pthru_host),
>  	STATS_DESC_COUNTER(VCPU, pthru_bad_aff)
>  };
> -static_assert(ARRAY_SIZE(kvm_vcpu_stats_desc) ==
> -		sizeof(struct kvm_vcpu_stat) / sizeof(u64));
>  
>  const struct kvm_stats_header kvm_vcpu_stats_header = {
>  	.name_size = KVM_STATS_NAME_SIZE,
> diff --git a/arch/powerpc/kvm/booke.c b/arch/powerpc/kvm/booke.c
> index 551b30d84aee..5ed6c235e059 100644
> --- a/arch/powerpc/kvm/booke.c
> +++ b/arch/powerpc/kvm/booke.c
> @@ -41,8 +41,6 @@ const struct _kvm_stats_desc kvm_vm_stats_desc[] = {
>  	STATS_DESC_ICOUNTER(VM, num_2M_pages),
>  	STATS_DESC_ICOUNTER(VM, num_1G_pages)
>  };
> -static_assert(ARRAY_SIZE(kvm_vm_stats_desc) ==
> -		sizeof(struct kvm_vm_stat) / sizeof(u64));
>  
>  const struct kvm_stats_header kvm_vm_stats_header = {
>  	.name_size = KVM_STATS_NAME_SIZE,
> @@ -79,8 +77,6 @@ const struct _kvm_stats_desc kvm_vcpu_stats_desc[] = {
>  	STATS_DESC_COUNTER(VCPU, pthru_host),
>  	STATS_DESC_COUNTER(VCPU, pthru_bad_aff)
>  };
> -static_assert(ARRAY_SIZE(kvm_vcpu_stats_desc) ==
> -		sizeof(struct kvm_vcpu_stat) / sizeof(u64));
>  
>  const struct kvm_stats_header kvm_vcpu_stats_header = {
>  	.name_size = KVM_STATS_NAME_SIZE,
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index 1695f0ced5ba..7610d33d319b 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -66,8 +66,6 @@ const struct _kvm_stats_desc kvm_vm_stats_desc[] = {
>  	STATS_DESC_COUNTER(VM, inject_service_signal),
>  	STATS_DESC_COUNTER(VM, inject_virtio)
>  };
> -static_assert(ARRAY_SIZE(kvm_vm_stats_desc) ==
> -		sizeof(struct kvm_vm_stat) / sizeof(u64));
>  
>  const struct kvm_stats_header kvm_vm_stats_header = {
>  	.name_size = KVM_STATS_NAME_SIZE,
> @@ -174,8 +172,6 @@ const struct _kvm_stats_desc kvm_vcpu_stats_desc[] = {
>  	STATS_DESC_COUNTER(VCPU, diagnose_other),
>  	STATS_DESC_COUNTER(VCPU, pfault_sync)
>  };
> -static_assert(ARRAY_SIZE(kvm_vcpu_stats_desc) ==
> -		sizeof(struct kvm_vcpu_stat) / sizeof(u64));
>  
>  const struct kvm_stats_header kvm_vcpu_stats_header = {
>  	.name_size = KVM_STATS_NAME_SIZE,
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 8166ad113fb2..b94a80ad5b8d 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -239,8 +239,6 @@ const struct _kvm_stats_desc kvm_vm_stats_desc[] = {
>  	STATS_DESC_ICOUNTER(VM, nx_lpage_splits),
>  	STATS_DESC_PCOUNTER(VM, max_mmu_page_hash_collisions)
>  };
> -static_assert(ARRAY_SIZE(kvm_vm_stats_desc) ==
> -		sizeof(struct kvm_vm_stat) / sizeof(u64));
>  
>  const struct kvm_stats_header kvm_vm_stats_header = {
>  	.name_size = KVM_STATS_NAME_SIZE,
> @@ -280,8 +278,6 @@ const struct _kvm_stats_desc kvm_vcpu_stats_desc[] = {
>  	STATS_DESC_COUNTER(VCPU, directed_yield_successful),
>  	STATS_DESC_ICOUNTER(VCPU, guest_mode)
>  };
> -static_assert(ARRAY_SIZE(kvm_vcpu_stats_desc) ==
> -		sizeof(struct kvm_vcpu_stat) / sizeof(u64));
>  
>  const struct kvm_stats_header kvm_vcpu_stats_header = {
>  	.name_size = KVM_STATS_NAME_SIZE,
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index ae7735b490b4..356af173114d 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -1273,56 +1273,66 @@ struct _kvm_stats_desc {
>  	char name[KVM_STATS_NAME_SIZE];
>  };
>  
> -#define STATS_DESC_COMMON(type, unit, base, exp)			       \
> +#define STATS_DESC_COMMON(type, unit, base, exp, sz, param)		       \
>  	.flags = type | unit | base |					       \
>  		 BUILD_BUG_ON_ZERO(type & ~KVM_STATS_TYPE_MASK) |	       \
>  		 BUILD_BUG_ON_ZERO(unit & ~KVM_STATS_UNIT_MASK) |	       \
>  		 BUILD_BUG_ON_ZERO(base & ~KVM_STATS_BASE_MASK),	       \
>  	.exponent = exp,						       \
> -	.size = 1
> +	.size = sz,							       \
> +	.hist_param = param
>  
> -#define VM_GENERIC_STATS_DESC(stat, type, unit, base, exp)		       \
> +#define VM_GENERIC_STATS_DESC(stat, type, unit, base, exp, sz, param)	       \
>  	{								       \
>  		{							       \
> -			STATS_DESC_COMMON(type, unit, base, exp),	       \
> +			STATS_DESC_COMMON(type, unit, base, exp, sz, param),   \
>  			.offset = offsetof(struct kvm_vm_stat, generic.stat)   \
>  		},							       \
>  		.name = #stat,						       \
>  	}
> -#define VCPU_GENERIC_STATS_DESC(stat, type, unit, base, exp)		       \
> +#define VCPU_GENERIC_STATS_DESC(stat, type, unit, base, exp, sz, param)	       \
>  	{								       \
>  		{							       \
> -			STATS_DESC_COMMON(type, unit, base, exp),	       \
> +			STATS_DESC_COMMON(type, unit, base, exp, sz, param),   \
>  			.offset = offsetof(struct kvm_vcpu_stat, generic.stat) \
>  		},							       \
>  		.name = #stat,						       \
>  	}
> -#define VM_STATS_DESC(stat, type, unit, base, exp)			       \
> +#define VM_STATS_DESC(stat, type, unit, base, exp, sz, param)		       \
>  	{								       \
>  		{							       \
> -			STATS_DESC_COMMON(type, unit, base, exp),	       \
> +			STATS_DESC_COMMON(type, unit, base, exp, sz, param),   \
>  			.offset = offsetof(struct kvm_vm_stat, stat)	       \
>  		},							       \
>  		.name = #stat,						       \
>  	}
> -#define VCPU_STATS_DESC(stat, type, unit, base, exp)			       \
> +#define VCPU_STATS_DESC(stat, type, unit, base, exp, sz, param)		       \
>  	{								       \
>  		{							       \
> -			STATS_DESC_COMMON(type, unit, base, exp),	       \
> +			STATS_DESC_COMMON(type, unit, base, exp, sz, param),   \
>  			.offset = offsetof(struct kvm_vcpu_stat, stat)	       \
>  		},							       \
>  		.name = #stat,						       \
>  	}
>  /* SCOPE: VM, VM_GENERIC, VCPU, VCPU_GENERIC */
> -#define STATS_DESC(SCOPE, stat, type, unit, base, exp)			       \
> -	SCOPE##_STATS_DESC(stat, type, unit, base, exp)
> +#define STATS_DESC(SCOPE, stat, type, unit, base, exp, sz, param)	       \
> +	SCOPE##_STATS_DESC(stat, type, unit, base, exp, sz, param)
>  
>  #define STATS_DESC_CUMULATIVE(SCOPE, name, unit, base, exponent)	       \
> -	STATS_DESC(SCOPE, name, KVM_STATS_TYPE_CUMULATIVE, unit, base, exponent)
> +	STATS_DESC(SCOPE, name, KVM_STATS_TYPE_CUMULATIVE,		       \
> +		unit, base, exponent, 1, 0)
>  #define STATS_DESC_INSTANT(SCOPE, name, unit, base, exponent)		       \
> -	STATS_DESC(SCOPE, name, KVM_STATS_TYPE_INSTANT, unit, base, exponent)
> +	STATS_DESC(SCOPE, name, KVM_STATS_TYPE_INSTANT,			       \
> +		unit, base, exponent, 1, 0)
>  #define STATS_DESC_PEAK(SCOPE, name, unit, base, exponent)		       \
> -	STATS_DESC(SCOPE, name, KVM_STATS_TYPE_PEAK, unit, base, exponent)
> +	STATS_DESC(SCOPE, name, KVM_STATS_TYPE_PEAK,			       \
> +		unit, base, exponent, 1, 0)
> +#define STATS_DESC_LINEAR_HIST(SCOPE, name, unit, base, exponent, sz, param)   \
> +	STATS_DESC(SCOPE, name, KVM_STATS_TYPE_LINEAR_HIST,		       \
> +		unit, base, exponent, sz, param)
> +#define STATS_DESC_LOG_HIST(SCOPE, name, unit, base, exponent, sz, param)      \
> +	STATS_DESC(SCOPE, name, KVM_STATS_TYPE_LOG_HIST,		       \
> +		unit, base, exponent, sz, param)
>  
>  /* Cumulative counter, read/write */
>  #define STATS_DESC_COUNTER(SCOPE, name)					       \
> @@ -1341,6 +1351,14 @@ struct _kvm_stats_desc {
>  #define STATS_DESC_TIME_NSEC(SCOPE, name)				       \
>  	STATS_DESC_CUMULATIVE(SCOPE, name, KVM_STATS_UNIT_SECONDS,	       \
>  		KVM_STATS_BASE_POW10, -9)
> +/* Linear histogram for time in nanosecond */
> +#define STATS_DESC_LINHIST_TIME_NSEC(SCOPE, name, sz, bucket_size)	       \
> +	STATS_DESC_LINEAR_HIST(SCOPE, name, KVM_STATS_UNIT_SECONDS,	       \
> +		KVM_STATS_BASE_POW10, -9, sz, bucket_size)
> +/* Logarithmic histogram for time in nanosecond */
> +#define STATS_DESC_LOGHIST_TIME_NSEC(SCOPE, name, sz)			       \
> +	STATS_DESC_LOG_HIST(SCOPE, name, KVM_STATS_UNIT_SECONDS,	       \
> +		KVM_STATS_BASE_POW10, -9, sz, LOGHIST_BASE_2)
>  
>  #define KVM_GENERIC_VM_STATS()						       \
>  	STATS_DESC_COUNTER(VM_GENERIC, remote_tlb_flush)
> @@ -1354,10 +1372,15 @@ struct _kvm_stats_desc {
>  	STATS_DESC_TIME_NSEC(VCPU_GENERIC, halt_poll_fail_ns)
>  
>  extern struct dentry *kvm_debugfs_dir;
> +
>  ssize_t kvm_stats_read(char *id, const struct kvm_stats_header *header,
>  		       const struct _kvm_stats_desc *desc,
>  		       void *stats, size_t size_stats,
>  		       char __user *user_buffer, size_t size, loff_t *offset);
> +void kvm_stats_linear_hist_update(u64 *data, size_t size,
> +				  u64 value, size_t bucket_size);
> +void kvm_stats_log_hist_update(u64 *data, size_t size, u64 value);
> +
>  extern const struct kvm_stats_header kvm_vm_stats_header;
>  extern const struct _kvm_stats_desc kvm_vm_stats_desc[];
>  extern const struct kvm_stats_header kvm_vcpu_stats_header;
> diff --git a/include/linux/kvm_types.h b/include/linux/kvm_types.h
> index ed6a985c5680..cc88cd676775 100644
> --- a/include/linux/kvm_types.h
> +++ b/include/linux/kvm_types.h
> @@ -76,6 +76,22 @@ struct kvm_mmu_memory_cache {
>  };
>  #endif
>  
> +/* Constants used for histogram stats */
> +#define LINHIST_SIZE_SMALL		10
> +#define LINHIST_SIZE_MEDIUM		20
> +#define LINHIST_SIZE_LARGE		50
> +#define LINHIST_SIZE_XLARGE		100

nit: s/SIZE/BUCKET_COUNT/

> +#define LINHIST_BUCKET_SIZE_SMALL	10
> +#define LINHIST_BUCKET_SIZE_MEDIUM	100
> +#define LINHIST_BUCKET_SIZE_LARGE	1000
> +#define LINHIST_BUCKET_SIZE_XLARGE	10000
> +
> +#define LOGHIST_SIZE_SMALL		8
> +#define LOGHIST_SIZE_MEDIUM		16
> +#define LOGHIST_SIZE_LARGE		32
> +#define LOGHIST_SIZE_XLARGE		64

Ditto here.

> +#define LOGHIST_BASE_2			2
> +
>  struct kvm_vm_stat_generic {
>  	u64 remote_tlb_flush;
>  };
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 68c9e6d8bbda..ff34a471d9ef 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -1963,7 +1963,9 @@ struct kvm_stats_header {
>  #define KVM_STATS_TYPE_CUMULATIVE	(0x0 << KVM_STATS_TYPE_SHIFT)
>  #define KVM_STATS_TYPE_INSTANT		(0x1 << KVM_STATS_TYPE_SHIFT)
>  #define KVM_STATS_TYPE_PEAK		(0x2 << KVM_STATS_TYPE_SHIFT)
> -#define KVM_STATS_TYPE_MAX		KVM_STATS_TYPE_PEAK
> +#define KVM_STATS_TYPE_LINEAR_HIST	(0x3 << KVM_STATS_TYPE_SHIFT)
> +#define KVM_STATS_TYPE_LOG_HIST		(0x4 << KVM_STATS_TYPE_SHIFT)
> +#define KVM_STATS_TYPE_MAX		KVM_STATS_TYPE_LOG_HIST
>  
>  #define KVM_STATS_UNIT_SHIFT		4
>  #define KVM_STATS_UNIT_MASK		(0xF << KVM_STATS_UNIT_SHIFT)
> @@ -1987,7 +1989,10 @@ struct kvm_stats_header {
>   *        Every data item is of type __u64.
>   * @offset: The offset of the stats to the start of stat structure in
>   *          struture kvm or kvm_vcpu.
> - * @unused: Unused field for future usage. Always 0 for now.
> + * @hist_param: A parameter value used for histogram stats. For linear
> + *              histogram stats, it indicates the size of the bucket;
> + *              For logarithmic histogram stats, it indicates the base
> + *              of the logarithm. Only base of 2 is supported.
>   * @name: The name string for the stats. Its size is indicated by the
>   *        &kvm_stats_header->name_size.
>   */
> @@ -1996,7 +2001,7 @@ struct kvm_stats_desc {
>  	__s16 exponent;
>  	__u16 size;
>  	__u32 offset;
> -	__u32 unused;
> +	__u32 hist_param;

`hist_param` is vague. What about making this an anonymous union to make
the dual meaning explicit?

        union {
                /* Only used for KVM_STATS_TYPE_LOG_HIST. */
                __u32 base;
                /* Only used for KVM_STATS_TYPE_LINEAR_HIST. */
                __u32 bucket_size;
        };

It may make the STATS_DESC code a bit more complicated but the rest of
the code that uses it will be much more clear.

>  	char name[];
>  };
>  
> diff --git a/virt/kvm/binary_stats.c b/virt/kvm/binary_stats.c
> index e609d428811a..6eead6979a7f 100644
> --- a/virt/kvm/binary_stats.c
> +++ b/virt/kvm/binary_stats.c
> @@ -144,3 +144,39 @@ ssize_t kvm_stats_read(char *id, const struct kvm_stats_header *header,
>  	*offset = pos;
>  	return len;
>  }
> +
> +/**
> + * kvm_stats_linear_hist_update() - Update bucket value for linear histogram
> + * statistics data.
> + *
> + * @data: start address of the stats data
> + * @size: the number of bucket of the stats data
> + * @value: the new value used to update the linear histogram's bucket
> + * @bucket_size: the size (width) of a bucket
> + */
> +void kvm_stats_linear_hist_update(u64 *data, size_t size,
> +				  u64 value, size_t bucket_size)
> +{
> +	size_t index = value / bucket_size;
> +
> +	if (index >= size)
> +		index = size - 1;

nit: It would be simpler to use max().

        size_t index = max(value / bucket_size, size - 1);

> +	++data[index];
> +}
> +
> +/**
> + * kvm_stats_log_hist_update() - Update bucket value for logarithmic histogram
> + * statistics data.
> + *
> + * @data: start address of the stats data
> + * @size: the number of bucket of the stats data
> + * @value: the new value used to update the logarithmic histogram's bucket
> + */
> +void kvm_stats_log_hist_update(u64 *data, size_t size, u64 value)
> +{
> +	size_t index = fls64(value);
> +
> +	if (index >= size)
> +		index = size - 1;

Ditto here about using max().

> +	++data[index];
> +}
> -- 
> 2.32.0.93.g670b81a890-goog
> 



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