Added option to manually specify a reference to compare the results to.

src/benchmark/relative_speed.rs

@@ -8,14 +8,16 @@ pub struct BenchmarkResultWithRelativeSpeed<'a> {
     pub result: &'a BenchmarkResult,
     pub relative_speed: Scalar,
     pub relative_speed_stddev: Option<Scalar>,
-    pub is_fastest: bool,
+    pub is_reference: bool,
+    // Less means faster
+    pub relative_ordering: Ordering,
 }
 
 pub fn compare_mean_time(l: &BenchmarkResult, r: &BenchmarkResult) -> Ordering {
     l.mean.partial_cmp(&r.mean).unwrap_or(Ordering::Equal)
 }
 
-fn fastest_of(results: &[BenchmarkResult]) -> &BenchmarkResult {
+pub fn fastest_of(results: &[BenchmarkResult]) -> &BenchmarkResult {
     results
         .iter()
         .min_by(|&l, &r| compare_mean_time(l, r))
@@ -24,32 +26,38 @@ fn fastest_of(results: &[BenchmarkResult]) -> &BenchmarkResult {
 
 fn compute_relative_speeds<'a>(
     results: &'a [BenchmarkResult],
-    fastest: &'a BenchmarkResult,
+    reference: &'a BenchmarkResult,
     sort_order: SortOrder,
 ) -> Vec<BenchmarkResultWithRelativeSpeed<'a>> {
     let mut results: Vec<_> = results
         .iter()
         .map(|result| {
-            let is_fastest = result == fastest;
+            let is_reference = result == reference;
+            let relative_ordering = compare_mean_time(result, reference);
 
             if result.mean == 0.0 {
                 return BenchmarkResultWithRelativeSpeed {
                     result,
-                    relative_speed: if is_fastest { 1.0 } else { f64::INFINITY },
+                    relative_speed: if is_reference { 1.0 } else { f64::INFINITY },
                     relative_speed_stddev: None,
-                    is_fastest,
+                    is_reference,
+                    relative_ordering,
                 };
             }
 
-            let ratio = result.mean / fastest.mean;
+            let ratio = match relative_ordering {
+                Ordering::Less => reference.mean / result.mean,
+                Ordering::Equal => 1.0,
+                Ordering::Greater => result.mean / reference.mean,
+            };
 
             // https://en.wikipedia.org/wiki/Propagation_of_uncertainty#Example_formulas
             // Covariance asssumed to be 0, i.e. variables are assumed to be independent
-            let ratio_stddev = match (result.stddev, fastest.stddev) {
+            let ratio_stddev = match (result.stddev, reference.stddev) {
                 (Some(result_stddev), Some(fastest_stddev)) => Some(
                     ratio
                         * ((result_stddev / result.mean).powi(2)
-                            + (fastest_stddev / fastest.mean).powi(2))
+                            + (fastest_stddev / reference.mean).powi(2))
                         .sqrt(),
                 ),
                 _ => None,
@@ -59,7 +67,8 @@ fn compute_relative_speeds<'a>(
                 result,
                 relative_speed: ratio,
                 relative_speed_stddev: ratio_stddev,
-                is_fastest,
+                is_reference,
+                relative_ordering,
             }
         })
         .collect();
@@ -74,6 +83,18 @@ fn compute_relative_speeds<'a>(
     results
 }
 
+pub fn compute_with_check_from_reference<'a>(
+    results: &'a [BenchmarkResult],
+    reference: &'a BenchmarkResult,
+    sort_order: SortOrder,
+) -> Option<Vec<BenchmarkResultWithRelativeSpeed<'a>>> {
+    if fastest_of(results).mean == 0.0 || reference.mean == 0.0 {
+        return None;
+    }
+
+    Some(compute_relative_speeds(results, reference, sort_order))
+}
+
 pub fn compute_with_check(
     results: &[BenchmarkResult],
     sort_order: SortOrder,
@@ -134,6 +155,20 @@ fn test_compute_relative_speed() {
     assert_relative_eq!(2.5, annotated_results[2].relative_speed);
 }
 
+#[test]
+fn test_compute_relative_speed_with_reference() {
+    use approx::assert_relative_eq;
+
+    let results = vec![create_result("cmd2", 2.0), create_result("cmd3", 5.0)];
+    let reference = create_result("cmd2", 4.0);
+
+    let annotated_results =
+        compute_with_check_from_reference(&results, &reference, SortOrder::Command).unwrap();
+
+    assert_relative_eq!(2.0, annotated_results[0].relative_speed);
+    assert_relative_eq!(1.25, annotated_results[1].relative_speed);
+}
+
 #[test]
 fn test_compute_relative_speed_for_zero_times() {
     let results = vec![create_result("cmd1", 1.0), create_result("cmd2", 0.0)];

src/benchmark/scheduler.rs

@@ -1,10 +1,10 @@
-use colored::*;
-
 use super::benchmark_result::BenchmarkResult;
 use super::executor::{Executor, MockExecutor, RawExecutor, ShellExecutor};
 use super::{relative_speed, Benchmark};
+use colored::*;
+use std::cmp::Ordering;
 
-use crate::command::Commands;
+use crate::command::{Command, Commands};
 use crate::export::ExportManager;
 use crate::options::{ExecutorKind, Options, OutputStyleOption, SortOrder};
 
@@ -38,9 +38,15 @@ impl<'a> Scheduler<'a> {
             ExecutorKind::Shell(ref shell) => Box::new(ShellExecutor::new(shell, self.options)),
         };
 
+        let reference = self
+            .options
+            .reference_command
+            .as_ref()
+            .map(|cmd| Command::new(None, cmd));
+
         executor.calibrate()?;
 
-        for (number, cmd) in self.commands.iter().enumerate() {
+        for (number, cmd) in reference.iter().chain(self.commands.iter()).enumerate() {
             self.results
                 .push(Benchmark::new(number, cmd, self.options, &*executor).run()?);
 
@@ -65,31 +71,56 @@ impl<'a> Scheduler<'a> {
             return;
         }
 
-        if let Some(annotated_results) = relative_speed::compute_with_check(
+        let reference = self
+            .options
+            .reference_command
+            .as_ref()
+            .map(|_| &self.results[0])
+            .unwrap_or_else(|| relative_speed::fastest_of(&self.results));
+
+        if let Some(annotated_results) = relative_speed::compute_with_check_from_reference(
             &self.results,
+            reference,
             self.options.sort_order_speed_comparison,
         ) {
             match self.options.sort_order_speed_comparison {
                 SortOrder::MeanTime => {
                     println!("{}", "Summary".bold());
 
-                    let fastest = annotated_results.iter().find(|r| r.is_fastest).unwrap();
-                    let others = annotated_results.iter().filter(|r| !r.is_fastest);
+                    let reference = annotated_results.iter().find(|r| r.is_reference).unwrap();
+                    let others = annotated_results.iter().filter(|r| !r.is_reference);
 
                     println!(
                         "  {} ran",
-                        fastest.result.command_with_unused_parameters.cyan()
+                        reference.result.command_with_unused_parameters.cyan()
                     );
 
                     for item in others {
+                        let stddev = if let Some(stddev) = item.relative_speed_stddev {
+                            format!(" ± {}", format!("{:.2}", stddev).green())
+                        } else {
+                            "".into()
+                        };
+                        let comparator = match item.relative_ordering {
+                            Ordering::Less => format!(
+                                "{}{} times slower than",
+                                format!("{:8.2}", item.relative_speed).bold().green(),
+                                stddev
+                            ),
+                            Ordering::Greater => format!(
+                                "{}{} times faster than",
+                                format!("{:8.2}", item.relative_speed).bold().green(),
+                                stddev
+                            ),
+                            Ordering::Equal => format!(
+                                "    As fast ({}{}) as",
+                                format!("{:.2}", item.relative_speed).bold().green(),
+                                stddev
+                            ),
+                        };
                         println!(
-                            "{}{} times faster than {}",
-                            format!("{:8.2}", item.relative_speed).bold().green(),
-                            if let Some(stddev) = item.relative_speed_stddev {
-                                format!(" ± {}", format!("{stddev:.2}").green())
-                            } else {
-                                "".into()
-                            },
+                            "{} {}",
+                            comparator,
                             &item.result.command_with_unused_parameters.magenta()
                         );
                     }
@@ -101,7 +132,7 @@ impl<'a> Scheduler<'a> {
                         println!(
                             "  {}{}  {}",
                             format!("{:10.2}", item.relative_speed).bold().green(),
-                            if item.is_fastest {
+                            if item.is_reference {
                                 "        ".into()
                             } else if let Some(stddev) = item.relative_speed_stddev {
                                 format!(" ± {}", format!("{stddev:5.2}").green())

src/cli.rs

@@ -86,6 +86,16 @@ fn build_command() -> Command {
                      not every time as would happen with the --prepare option."
                 ),
         )
+        .arg(
+            Arg::new("reference")
+                .long("reference")
+                .action(ArgAction::Set)
+                .value_name("CMD")
+                .help(
+                    "The reference command for the relative comparison of results. \
+                    If this is unset, results are compared with the fastest command as reference."
+                )
+        )
         .arg(
             Arg::new("prepare")
                 .long("prepare")

src/export/markup.rs

@@ -56,7 +56,7 @@ pub trait MarkupExporter {
             let min_str = format_duration_value(measurement.min, Some(unit)).0;
             let max_str = format_duration_value(measurement.max, Some(unit)).0;
             let rel_str = format!("{:.2}", entry.relative_speed);
-            let rel_stddev_str = if entry.is_fastest {
+            let rel_stddev_str = if entry.is_reference {
                 "".into()
             } else if let Some(stddev) = entry.relative_speed_stddev {
                 format!(" ± {stddev:.2}")

src/options.rs

@@ -204,6 +204,9 @@ pub struct Options {
     /// Whether or not to ignore non-zero exit codes
     pub command_failure_action: CmdFailureAction,
 
+    // Command to use as a reference for relative speed comparison
+    pub reference_command: Option<String>,
+
     /// Command(s) to run before each timing run
     pub preparation_command: Option<Vec<String>>,
 
@@ -245,6 +248,7 @@ impl Default for Options {
             warmup_count: 0,
             min_benchmarking_time: 3.0,
             command_failure_action: CmdFailureAction::RaiseError,
+            reference_command: None,
             preparation_command: None,
             conclusion_command: None,
             setup_command: None,
@@ -304,6 +308,8 @@ impl Options {
 
         options.setup_command = matches.get_one::<String>("setup").map(String::from);
 
+        options.reference_command = matches.get_one::<String>("reference").map(String::from);
+
         options.preparation_command = matches
             .get_many::<String>("prepare")
             .map(|values| values.map(String::from).collect::<Vec<String>>());
@@ -431,21 +437,25 @@ impl Options {
     }
 
     pub fn validate_against_command_list(&self, commands: &Commands) -> Result<()> {
+        let num_commands = commands.num_commands()
+            + if self.reference_command.is_some() {
+                1
+            } else {
+                0
+            };
         if let Some(preparation_command) = &self.preparation_command {
             ensure!(
-                preparation_command.len() <= 1
-                    || commands.num_commands() == preparation_command.len(),
+                preparation_command.len() <= 1 || num_commands == preparation_command.len(),
                 "The '--prepare' option has to be provided just once or N times, where N is the \
-             number of benchmark commands."
+             number of benchmark commands including a potential reference."
             );
         }
 
         if let Some(conclusion_command) = &self.conclusion_command {
             ensure!(
-                conclusion_command.len() <= 1
-                    || commands.num_commands() == conclusion_command.len(),
+                conclusion_command.len() <= 1 || num_commands == conclusion_command.len(),
                 "The '--conclude' option has to be provided just once or N times, where N is the \
-             number of benchmark commands."
+             number of benchmark commands including a potential reference."
             );
         }