func WithDuration(i int) Options {
	return func(o *Config) {
		o.Duration = i
	}
}
WithDuration set the test running duration
package perfm
type Config struct {
	Duration       int     `json:"duration"`          
	Parallel       int     `json:"parallel"`          
	Number         int     `json:"number"`            
	NoPrint        bool    `json:"no_print"`          
	Frequency      int     `json:"frequency"`         
	BufferSize     int     `json:"buffer_size"`       
	BinsNumber     int     `json:"bins_number"`       
	GrowthFactor   float64 `json:"growth_factor"`     
	MinValue       int64   `json:"min_value"`         
	BaseBucketSize float64 `json:"base_bucket_size"`  
}
func newConfig(options ...Options) Config {
	c := Config{10, 4, 0, false, 1, 6553500, 15, 1.4, 1000000, 1000000}
	for _, o := range options {
		o(&c)
	}
	return c
}
type Options func(*Config)
func WithParallel(i int) Options {
	return func(o *Config) {
		o.Parallel = i
	}
}