From ce28485be256461c5819433dc0ab8137956dafcd Mon Sep 17 00:00:00 2001
From: Benson Wong <mostlygeek@gmail.com>
Date: Sat, 25 Apr 2026 16:13:07 -0700
Subject: [PATCH] ui-svelte: add prompt processing histogram (#705)

Activities page shows histograms for prompt processing and token generation times.

Fix: #691
Fix: #703
---
 ui-svelte/src/components/ActivityStats.svelte | 77 ++++++++++++-------
 ui-svelte/src/components/Header.svelte        |  8 +-
 .../src/components/TokenHistogram.svelte      | 48 ++++++++++--
 ui-svelte/src/lib/histogram.test.ts           | 24 +++---
 ui-svelte/src/lib/histogram.ts                | 11 ++-
 ui-svelte/src/routes/Activity.svelte          |  1 -
 6 files changed, 117 insertions(+), 52 deletions(-)

diff --git a/ui-svelte/src/components/ActivityStats.svelte b/ui-svelte/src/components/ActivityStats.svelte
index 527967d3..316d2abe 100644
--- a/ui-svelte/src/components/ActivityStats.svelte
+++ b/ui-svelte/src/components/ActivityStats.svelte
@@ -11,57 +11,82 @@
     const totalRequests = $metrics.length;
     const totalInputTokens = $metrics.reduce((sum, m) => sum + m.input_tokens, 0);
     const totalOutputTokens = $metrics.reduce((sum, m) => sum + m.output_tokens, 0);
+    const totalCacheTokens = $metrics.reduce((sum, m) => sum + m.cache_tokens, 0);
 
-    const tokensPerSecond = $metrics
-      .filter((m) => m.tokens_per_second > 0)
-      .map((m) => m.tokens_per_second);
+    const promptPerSecond = $metrics.filter((m) => m.prompt_per_second > 0).map((m) => m.prompt_per_second);
 
-    const histogramData = tokensPerSecond.length > 0
-      ? calculateHistogramData(tokensPerSecond, { minBins: 20, maxBins: 80, binScaling: 3 })
-      : null;
+    const tokensPerSecond = $metrics.filter((m) => m.tokens_per_second > 0).map((m) => m.tokens_per_second);
+
+    const promptHistogramData =
+      promptPerSecond.length > 0 ? calculateHistogramData(promptPerSecond) : null;
+
+    const genHistogramData =
+      tokensPerSecond.length > 0 ? calculateHistogramData(tokensPerSecond) : null;
 
     return {
       totalRequests,
       totalInputTokens,
       totalOutputTokens,
+      totalCacheTokens,
       inFlightRequests: $inFlightRequests,
-      histogramData,
+      promptHistogramData,
+      genHistogramData,
     };
   });
 </script>
 
-<div class="card">
+<div class="card relative p-3">
   <button
-    class="flex items-center gap-1 px-4 pt-3 text-xs font-medium text-gray-500 dark:text-gray-400 hover:text-gray-700 dark:hover:text-gray-200 transition-colors"
-    onclick={() => $histogramCollapsed = !$histogramCollapsed}
+    class="absolute top-2 right-2 w-6 h-6 flex items-center justify-center rounded-full border border-gray-300 dark:border-gray-600 text-gray-400 dark:text-gray-500 hover:text-gray-600 dark:hover:text-gray-300 hover:border-gray-400 dark:hover:border-gray-400 transition-colors"
+    onclick={() => ($histogramCollapsed = !$histogramCollapsed)}
+    title={$histogramCollapsed ? "Show histograms" : "Hide histograms"}
   >
-    <svg
-      class="w-3 h-3 transition-transform"
-      style="transform: rotate({$histogramCollapsed ? -90 : 0}deg)"
-      viewBox="0 0 16 16"
-      fill="currentColor"
-    >
-      <path d="M4.5 6l3.5 4 3.5-4H4.5z" />
-    </svg>
-    Tokens/sec Distribution
+    {#if $histogramCollapsed}
+      <svg class="w-3.5 h-3.5" viewBox="0 0 16 16" fill="currentColor">
+        <path d="M4.5 6l3.5 4 3.5-4H4.5z" />
+      </svg>
+    {:else}
+      <svg class="w-3 h-3" viewBox="0 0 16 16" fill="currentColor">
+        <path d="M3.5 3.5l9 9M12.5 3.5l-9 9" stroke="currentColor" stroke-width="2" stroke-linecap="round" fill="none" />
+      </svg>
+    {/if}
   </button>
   {#if !$histogramCollapsed}
-    {#if stats.histogramData}
-      <TokenHistogram data={stats.histogramData} />
-    {:else}
-      <div class="px-4 py-6 text-center text-sm text-gray-500 dark:text-gray-400">
-        No token speed data yet
+    <div class="flex flex-col sm:flex-row gap-6 mb-3">
+      <div class="w-full sm:w-1/2 min-w-0">
+        <div class="text-sm font-medium text-gray-500 dark:text-gray-400 mb-1">Prompt Processing</div>
+        {#if stats.promptHistogramData}
+          <TokenHistogram
+            data={stats.promptHistogramData}
+            unit="prompt tokens/sec"
+            colorClass="text-amber-500 dark:text-amber-400"
+          />
+        {:else}
+          <div class="py-6 text-center text-sm text-gray-500 dark:text-gray-400">No prompt speed data yet</div>
+        {/if}
       </div>
-    {/if}
+      <div class="w-full sm:w-1/2 min-w-0">
+        <div class="text-sm font-medium text-gray-500 dark:text-gray-400 mb-1">Token Generation</div>
+        {#if stats.genHistogramData}
+          <TokenHistogram data={stats.genHistogramData} unit="tokens/sec" />
+        {:else}
+          <div class="py-6 text-center text-sm text-gray-500 dark:text-gray-400">No generation speed data yet</div>
+        {/if}
+      </div>
+    </div>
   {/if}
-  <div class="grid grid-cols-3 gap-x-6 gap-y-1 px-4 pb-3 text-sm">
+  <div class="grid grid-cols-4 gap-x-6 gap-y-1 text-sm">
     <div class="text-xs uppercase tracking-wider text-gray-500 dark:text-gray-400">Requests</div>
+    <div class="text-xs uppercase tracking-wider text-gray-500 dark:text-gray-400">Cached</div>
     <div class="text-xs uppercase tracking-wider text-gray-500 dark:text-gray-400">Processed</div>
     <div class="text-xs uppercase tracking-wider text-gray-500 dark:text-gray-400">Generated</div>
     <div class="text-sm text-gray-700 dark:text-gray-300">
       <span class="font-semibold">{nf.format(stats.totalRequests)}</span> completed,
       <span class="font-semibold">{nf.format(stats.inFlightRequests)}</span> waiting
     </div>
+    <div class="text-sm text-gray-700 dark:text-gray-300">
+      <span class="font-semibold">{nf.format(stats.totalCacheTokens)}</span> tokens
+    </div>
     <div class="text-sm text-gray-700 dark:text-gray-300">
       <span class="font-semibold">{nf.format(stats.totalInputTokens)}</span> tokens
     </div>
diff --git a/ui-svelte/src/components/Header.svelte b/ui-svelte/src/components/Header.svelte
index c3cf4a8f..1c9529d0 100644
--- a/ui-svelte/src/components/Header.svelte
+++ b/ui-svelte/src/components/Header.svelte
@@ -50,7 +50,7 @@
     <a
       href="/"
       use:link
-      class="p-1 whitespace-nowrap {isActive('/', $currentRoute) ? 'font-semibold' : ''} {$playgroundActivity ? 'activity-link' : 'text-gray-600 hover:text-black dark:text-gray-300 dark:hover:text-gray-100'}"
+      class="p-1 whitespace-nowrap {isActive('/', $currentRoute) ? 'font-semibold underline underline-offset-4' : ''} {$playgroundActivity ? 'activity-link' : 'text-gray-600 hover:text-black dark:text-gray-300 dark:hover:text-gray-100'}"
     >
       Playground
     </a>
@@ -59,6 +59,8 @@
       use:link
       class="text-gray-600 hover:text-black dark:text-gray-300 dark:hover:text-gray-100 p-1 whitespace-nowrap"
       class:font-semibold={isActive("/models", $currentRoute)}
+      class:underline={isActive("/models", $currentRoute)}
+      class:underline-offset-4={isActive("/models", $currentRoute)}
     >
       Models
     </a>
@@ -67,6 +69,8 @@
       use:link
       class="text-gray-600 hover:text-black dark:text-gray-300 dark:hover:text-gray-100 p-1 whitespace-nowrap"
       class:font-semibold={isActive("/activity", $currentRoute)}
+      class:underline={isActive("/activity", $currentRoute)}
+      class:underline-offset-4={isActive("/activity", $currentRoute)}
     >
       Activity
     </a>
@@ -75,6 +79,8 @@
       use:link
       class="text-gray-600 hover:text-black dark:text-gray-300 dark:hover:text-gray-100 p-1 whitespace-nowrap"
       class:font-semibold={isActive("/logs", $currentRoute)}
+      class:underline={isActive("/logs", $currentRoute)}
+      class:underline-offset-4={isActive("/logs", $currentRoute)}
     >
       Logs
     </a>
diff --git a/ui-svelte/src/components/TokenHistogram.svelte b/ui-svelte/src/components/TokenHistogram.svelte
index 0d4fc45d..4a6ed57b 100644
--- a/ui-svelte/src/components/TokenHistogram.svelte
+++ b/ui-svelte/src/components/TokenHistogram.svelte
@@ -1,10 +1,18 @@
 <script lang="ts">
   import type { HistogramData } from "../lib/types";
 
-  let { data }: { data: HistogramData } = $props();
+  let {
+    data,
+    unit = "tokens/sec",
+    colorClass = "text-blue-500 dark:text-blue-400",
+  }: {
+    data: HistogramData;
+    unit?: string;
+    colorClass?: string;
+  } = $props();
 
-  const height = 55;
-  const padding = { top: 5, right: 45, bottom: 15, left: 45 };
+  const height = 250;
+  const padding = { top: 30, right: 20, bottom: 40, left: 75 };
   const viewBoxWidth = 1200;
   const chartWidth = viewBoxWidth - padding.left - padding.right;
   const chartHeight = height - padding.top - padding.bottom;
@@ -31,6 +39,24 @@
       opacity="0.3"
     />
 
+    <!-- Y-axis ticks and labels -->
+    {#each [0, 0.5, 1] as fraction}
+      {@const tickCount = Math.round(maxCount * fraction)}
+      {@const tickY = height - padding.bottom - fraction * chartHeight}
+      <line
+        x1={padding.left - 8}
+        y1={tickY}
+        x2={padding.left}
+        y2={tickY}
+        stroke="currentColor"
+        stroke-width="1"
+        opacity="0.4"
+      />
+      <text x={padding.left - 10} y={tickY + 10} font-size="26" fill="currentColor" opacity="0.8" text-anchor="end">
+        {tickCount}
+      </text>
+    {/each}
+
     <!-- X-axis -->
     <line
       x1={padding.left}
@@ -57,9 +83,9 @@
           height={barHeight}
           fill="currentColor"
           opacity="0.6"
-          class="text-blue-500 dark:text-blue-400 hover:opacity-90 transition-opacity cursor-pointer"
+          class="{colorClass} hover:opacity-90 transition-opacity cursor-pointer"
         />
-        <title>{`${binStart.toFixed(1)} - ${binEnd.toFixed(1)} tokens/sec\nCount: ${count}`}</title>
+        <title>{`${binStart.toFixed(1)} - ${binEnd.toFixed(1)} ${unit}\nCount: ${count}`}</title>
       </g>
     {/each}
 
@@ -101,13 +127,19 @@
     />
 
     <!-- X-axis labels -->
-    <text x={padding.left} y={height - 5} font-size="10" fill="currentColor" opacity="0.6" text-anchor="start">
+    <text x={padding.left} y={height - 8} font-size="26" fill="currentColor" opacity="0.8" text-anchor="start">
       {data.min.toFixed(1)}
     </text>
 
-    <text x={viewBoxWidth - padding.right} y={height - 5} font-size="10" fill="currentColor" opacity="0.6" text-anchor="end">
+    <text
+      x={viewBoxWidth - padding.right}
+      y={height - 8}
+      font-size="26"
+      fill="currentColor"
+      opacity="0.8"
+      text-anchor="end"
+    >
       {data.max.toFixed(1)}
     </text>
-
   </svg>
 </div>
diff --git a/ui-svelte/src/lib/histogram.test.ts b/ui-svelte/src/lib/histogram.test.ts
index fbfd5080..77f3bf45 100644
--- a/ui-svelte/src/lib/histogram.test.ts
+++ b/ui-svelte/src/lib/histogram.test.ts
@@ -52,14 +52,14 @@ describe("calculateHistogramData", () => {
       const values = Array.from({ length: 100 }, (_, i) => i);
       const result = calculateHistogramData(values);
       expect(result).not.toBeNull();
-      expect(result!.bins.length).toBe(20);
+      expect(result!.bins.length).toBe(8);
       const binSum = result!.bins.reduce((s, b) => s + b, 0);
       expect(binSum).toBe(100);
     });
 
     it("places values in correct bins", () => {
       const values = [1, 1, 1, 5, 5, 9, 9, 9];
-      const result = calculateHistogramData(values, { minBins: 3, maxBins: 3, binScaling: 1 });
+      const result = calculateHistogramData(values, { minBins: 3, maxBins: 3 });
       expect(result).not.toBeNull();
       expect(result!.bins.length).toBe(3);
       expect(result!.bins.reduce((s, b) => s + b, 0)).toBe(8);
@@ -114,27 +114,31 @@ describe("calculateHistogramData", () => {
 
   describe("bin count adaptation", () => {
     it("uses minimum bins for small datasets", () => {
-      const values = Array.from({ length: 20 }, (_, i) => i);
+      // n=8: sturges=4, clamped up to minBins=5
+      const values = Array.from({ length: 8 }, (_, i) => i);
       const result = calculateHistogramData(values);
-      expect(result!.bins.length).toBe(10);
+      expect(result!.bins.length).toBe(5);
     });
 
     it("scales bins with dataset size", () => {
+      // n=100: sturges=8
       const values = Array.from({ length: 100 }, (_, i) => i);
       const result = calculateHistogramData(values);
-      expect(result!.bins.length).toBe(20);
+      expect(result!.bins.length).toBe(8);
     });
 
     it("caps bins at maximum", () => {
-      const values = Array.from({ length: 200 }, (_, i) => i);
-      const result = calculateHistogramData(values);
-      expect(result!.bins.length).toBe(30);
+      // n=1000: sturges=11, clamped down to maxBins=10
+      const values = Array.from({ length: 1000 }, (_, i) => i);
+      const result = calculateHistogramData(values, { minBins: 5, maxBins: 10 });
+      expect(result!.bins.length).toBe(10);
     });
 
     it("respects custom options", () => {
+      // n=100: sturges=8, within [minBins=5, maxBins=10]
       const values = Array.from({ length: 100 }, (_, i) => i);
-      const result = calculateHistogramData(values, { minBins: 5, maxBins: 10, binScaling: 2 });
-      expect(result!.bins.length).toBe(10);
+      const result = calculateHistogramData(values, { minBins: 5, maxBins: 10 });
+      expect(result!.bins.length).toBe(8);
     });
   });
 
diff --git a/ui-svelte/src/lib/histogram.ts b/ui-svelte/src/lib/histogram.ts
index f9c405d0..f3863621 100644
--- a/ui-svelte/src/lib/histogram.ts
+++ b/ui-svelte/src/lib/histogram.ts
@@ -3,13 +3,11 @@ import type { HistogramData } from "./types";
 export interface HistogramOptions {
   minBins?: number;
   maxBins?: number;
-  binScaling?: number;
 }
 
 const DEFAULT_OPTIONS: HistogramOptions = {
-  minBins: 10,
-  maxBins: 30,
-  binScaling: 5,
+  minBins: 5,
+  maxBins: 20,
 };
 
 function percentile(sorted: number[], p: number): number {
@@ -50,8 +48,9 @@ export function calculateHistogramData(
     };
   }
 
-  const { minBins = 10, maxBins = 30, binScaling = 5 } = options;
-  const binCount = Math.min(maxBins, Math.max(minBins, Math.floor(values.length / binScaling)));
+  const { minBins = 5, maxBins = 20 } = options;
+  const sturges = Math.ceil(Math.log2(values.length)) + 1;
+  const binCount = Math.min(maxBins, Math.max(minBins, sturges));
   const binSize = (max - min) / binCount;
 
   const bins = new Array(binCount).fill(0);
diff --git a/ui-svelte/src/routes/Activity.svelte b/ui-svelte/src/routes/Activity.svelte
index b81990a9..3790cf70 100644
--- a/ui-svelte/src/routes/Activity.svelte
+++ b/ui-svelte/src/routes/Activity.svelte
@@ -63,7 +63,6 @@
 </script>
 
 <div class="p-2">
-  <h1 class="text-2xl font-bold">Activity</h1>
   <div class="mt-4 mb-4">
     <ActivityStats />
   </div>