feat(inputs.modbus): Optimise grouped requests

plugins/inputs/modbus/README.md

@@ -147,11 +147,21 @@ See the [CONFIGURATION.md][CONFIGURATION.md] for more details.
     ##  |                 to reduce the number of requested registers by keeping
     ##  |                 the number of requests.
     ##  |---aggressive -- Rearrange request boundaries similar to "rearrange" but
-    ##                    allow to request registers not specified by the user to
-    ##                    fill gaps. This usually reduces the number of requests at the
-    ##                    cost of more requested registers.
+    ##  |                 allow to request registers not specified by the user to
+    ##  |                 fill gaps. This usually reduces the number of requests at the
+    ##  |                 cost of more requested registers.
+    ##  |---max_insert -- Rearrange request keeping the number of extra fields below the value
+    ##                    provided in "optimization_max_register_fill". It is not necessary to define 'omitted'
+    ##                    fields as the optimisation will add such field only where needed.
     # optimization = "none"
 
+    ## Maximum number register the optimizer is allowed to insert between two fields to 
+    ## save requests.
+    ## This option is only used for the 'max_insert' optimization strategy.
+    ## NOTE: All omitted fields are ignored, so this option denotes the effective hole 
+    ## size to fill.
+    # optimization_max_register_fill = 50
+
     ## Field definitions
     ## Analog Variables, Input Registers and Holding Registers
     ## address        - address of the register to query. For coil and discrete inputs this is the bit address.
@@ -397,6 +407,23 @@ interested in but want to minimize the number of requests sent to the device.
 __Please note:__ This optimization might take long in case of many
 non-consecutive, non-omitted fields!
 
+##### `max_insert`
+
+Fields are assigned to the same request as long as the hole between the fields
+do not exceed the maximum fill size given in `optimization_max_register_fill`.
+User-defined omitted fields are ignored and interpreted as holes, so the best
+practice is to not manually insert omitted fields for this optimizer. This
+allows to specify only actually used fields and let the optimizer figure out
+the request organization which can dramatically improve query time. The
+trade-off here is between the cost of reading additional registers trashed
+later and the cost of many requests.
+
+__Please note:__ The optimal value for `optimization_max_register_fill` depends
+on the network and the queried device. It is hence recommended to test several
+values and assess performance in order to find the best value. Use the
+`--test --debug` flags to monitor how may requests are sent and the number of
+touched registers.
+
 #### Field definitions
 
 Each `request` can contain a list of fields to collect from the modbus device.

plugins/inputs/modbus/configuration_register.go

@@ -95,7 +95,7 @@ func (c *ConfigurationOriginal) initRequests(fieldDefs []fieldDefinition, maxQua
 	if err != nil {
 		return nil, err
 	}
-	return groupFieldsToRequests(fields, nil, maxQuantity, "none"), nil
+	return groupFieldsToRequests(fields, nil, maxQuantity, "none", 0), nil
 }
 
 func (c *ConfigurationOriginal) initFields(fieldDefs []fieldDefinition) ([]field, error) {

plugins/inputs/modbus/configuration_request.go

@@ -5,8 +5,6 @@ import (
 	"errors"
 	"fmt"
 	"hash/maphash"
-
-	"github.com/influxdata/telegraf/internal/choice"
 )
 
 //go:embed sample_request.conf
@@ -23,13 +21,14 @@ type requestFieldDefinition struct {
 }
 
 type requestDefinition struct {
-	SlaveID      byte                     `toml:"slave_id"`
-	ByteOrder    string                   `toml:"byte_order"`
-	RegisterType string                   `toml:"register"`
-	Measurement  string                   `toml:"measurement"`
-	Optimization string                   `toml:"optimization"`
-	Fields       []requestFieldDefinition `toml:"fields"`
-	Tags         map[string]string        `toml:"tags"`
+	SlaveID           byte                     `toml:"slave_id"`
+	ByteOrder         string                   `toml:"byte_order"`
+	RegisterType      string                   `toml:"register"`
+	Measurement       string                   `toml:"measurement"`
+	Optimization      string                   `toml:"optimization"`
+	MaxExtraRegisters uint16                   `toml:"optimization_max_register_fill"`
+	Fields            []requestFieldDefinition `toml:"fields"`
+	Tags              map[string]string        `toml:"tags"`
 }
 
 type ConfigurationPerRequest struct {
@@ -46,12 +45,6 @@ func (c *ConfigurationPerRequest) Check() error {
 	seenFields := make(map[uint64]bool)
 
 	for _, def := range c.Requests {
-		// Check for valid optimization
-		validOptimizations := []string{"", "none", "shrink", "rearrange", "aggressive"}
-		if !choice.Contains(def.Optimization, validOptimizations) {
-			return fmt.Errorf("unknown optimization %q", def.Optimization)
-		}
-
 		// Check byte order of the data
 		switch def.ByteOrder {
 		case "":
@@ -69,7 +62,31 @@ func (c *ConfigurationPerRequest) Check() error {
 		default:
 			return fmt.Errorf("unknown register-type %q", def.RegisterType)
 		}
-
+		// Check for valid optimization
+		switch def.Optimization {
+		case "", "none", "shrink", "rearrange", "aggressive":
+		case "max_insert":
+			switch def.RegisterType {
+			case "coil":
+				if def.MaxExtraRegisters <= 0 || def.MaxExtraRegisters > maxQuantityCoils {
+					return fmt.Errorf("optimization_max_register_fill has to be between 1 and %d", maxQuantityCoils)
+				}
+			case "discrete":
+				if def.MaxExtraRegisters <= 0 || def.MaxExtraRegisters > maxQuantityDiscreteInput {
+					return fmt.Errorf("optimization_max_register_fill has to be between 1 and %d", maxQuantityDiscreteInput)
+				}
+			case "holding":
+				if def.MaxExtraRegisters <= 0 || def.MaxExtraRegisters > maxQuantityHoldingRegisters {
+					return fmt.Errorf("optimization_max_register_fill has to be between 1 and %d", maxQuantityHoldingRegisters)
+				}
+			case "input":
+				if def.MaxExtraRegisters <= 0 || def.MaxExtraRegisters > maxQuantityInputRegisters {
+					return fmt.Errorf("optimization_max_register_fill has to be between 1 and %d", maxQuantityInputRegisters)
+				}
+			}
+		default:
+			return fmt.Errorf("unknown optimization %q", def.Optimization)
+		}
 		// Set the default for measurement if required
 		if def.Measurement == "" {
 			def.Measurement = "modbus"
@@ -167,28 +184,28 @@ func (c *ConfigurationPerRequest) Process() (map[byte]requestSet, error) {
 			if c.workarounds.OnRequestPerField {
 				maxQuantity = 1
 			}
-			requests := groupFieldsToRequests(fields, def.Tags, maxQuantity, def.Optimization)
+			requests := groupFieldsToRequests(fields, def.Tags, maxQuantity, def.Optimization, def.MaxExtraRegisters)
 			set.coil = append(set.coil, requests...)
 		case "discrete":
 			maxQuantity := maxQuantityDiscreteInput
 			if c.workarounds.OnRequestPerField {
 				maxQuantity = 1
 			}
-			requests := groupFieldsToRequests(fields, def.Tags, maxQuantity, def.Optimization)
+			requests := groupFieldsToRequests(fields, def.Tags, maxQuantity, def.Optimization, def.MaxExtraRegisters)
 			set.discrete = append(set.discrete, requests...)
 		case "holding":
 			maxQuantity := maxQuantityHoldingRegisters
 			if c.workarounds.OnRequestPerField {
 				maxQuantity = 1
 			}
-			requests := groupFieldsToRequests(fields, def.Tags, maxQuantity, def.Optimization)
+			requests := groupFieldsToRequests(fields, def.Tags, maxQuantity, def.Optimization, def.MaxExtraRegisters)
 			set.holding = append(set.holding, requests...)
 		case "input":
 			maxQuantity := maxQuantityInputRegisters
 			if c.workarounds.OnRequestPerField {
 				maxQuantity = 1
 			}
-			requests := groupFieldsToRequests(fields, def.Tags, maxQuantity, def.Optimization)
+			requests := groupFieldsToRequests(fields, def.Tags, maxQuantity, def.Optimization, def.MaxExtraRegisters)
 			set.input = append(set.input, requests...)
 		default:
 			return nil, fmt.Errorf("unknown register type %q", def.RegisterType)

plugins/inputs/modbus/modbus.go

@@ -138,7 +138,35 @@ func (m *Modbus) Init() error {
 	if err := m.initClient(); err != nil {
 		return fmt.Errorf("initializing client failed: %v", err)
 	}
+	for slaveID, rqs := range m.requests {
+		var nHoldingRegs, nInputsRegs, nDiscreteRegs, nCoilRegs uint16
+		var nHoldingFields, nInputsFields, nDiscreteFields, nCoilFields int
 
+		for _, r := range rqs.holding {
+			nHoldingRegs += r.length
+			nHoldingFields += len(r.fields)
+		}
+		for _, r := range rqs.input {
+			nInputsRegs += r.length
+			nInputsFields += len(r.fields)
+		}
+		for _, r := range rqs.discrete {
+			nDiscreteRegs += r.length
+			nDiscreteFields += len(r.fields)
+		}
+		for _, r := range rqs.coil {
+			nCoilRegs += r.length
+			nCoilFields += len(r.fields)
+		}
+		m.Log.Infof("Got %d request(s) touching %d holding registers for %d fields (slave %d)",
+			len(rqs.holding), nHoldingRegs, nHoldingFields, slaveID)
+		m.Log.Infof("Got %d request(s) touching %d inputs registers for %d fields (slave %d)",
+			len(rqs.input), nInputsRegs, nInputsFields, slaveID)
+		m.Log.Infof("Got %d request(s) touching %d discrete registers for %d fields (slave %d)",
+			len(rqs.discrete), nDiscreteRegs, nDiscreteFields, slaveID)
+		m.Log.Infof("Got %d request(s) touching %d coil registers for %d fields (slave %d)",
+			len(rqs.coil), nCoilRegs, nCoilFields, slaveID)
+	}
 	return nil
 }