Analyze CPU Cache Efficiency and Memory Access Latency
Calculation Results:
Total Memory Accesses:
Cache Miss Rate:
Cache Hit Rate:
Average Memory Access Time (AMAT):
How to Calculate Cache Miss Rate
In computer architecture, the cache miss rate is a critical metric that measures the efficiency of a CPU's cache memory system. It represents the fraction of memory accesses that are not found in the cache and must therefore be fetched from a slower level of memory (like RAM).
The Cache Miss Rate Formula
To calculate the miss rate, you use the following mathematical formula:
Miss Rate = (Total Misses / (Total Hits + Total Misses)) × 100%
Understanding the Components
Cache Hit: When the processor finds the requested data in the cache. This is fast.
Cache Miss: When the data is not in the cache, requiring a fetch from main memory. This causes latency.
Hit Rate: The percentage of accesses that result in a hit (100% – Miss Rate).
Average Memory Access Time (AMAT): A performance calculation that factors in hit time and miss penalties.
Realistic Calculation Example
Imagine a processor executing a program that performs 1,000 memory requests. If 920 of those requests are found in the L1 cache and 80 result in misses:
Total Accesses: 920 + 80 = 1,000
Miss Rate: (80 / 1,000) = 0.08 or 8%
Hit Rate: (920 / 1,000) = 0.92 or 92%
If the Hit Time is 1 cycle and the Miss Penalty is 100 cycles, the AMAT would be: 1 + (0.08 × 100) = 9 cycles per access.
function calculateCacheStats() {
var hits = parseFloat(document.getElementById('cacheHits').value);
var misses = parseFloat(document.getElementById('cacheMisses').value);
var hTime = parseFloat(document.getElementById('hitTime').value);
var mPenalty = parseFloat(document.getElementById('missPenalty').value);
// Validation
if (isNaN(hits) || isNaN(misses) || hits < 0 || misses < 0) {
alert("Please enter valid positive numbers for hits and misses.");
return;
}
var totalAccesses = hits + misses;
if (totalAccesses === 0) {
alert("Total accesses cannot be zero.");
return;
}
var missRate = (misses / totalAccesses) * 100;
var hitRate = (hits / totalAccesses) * 100;
// Display basic results
document.getElementById('resTotal').innerText = totalAccesses.toLocaleString();
document.getElementById('resMissRate').innerText = missRate.toFixed(2) + "%";
document.getElementById('resHitRate').innerText = hitRate.toFixed(2) + "%";
// AMAT Calculation
if (!isNaN(hTime) && !isNaN(mPenalty)) {
var amat = hTime + ((misses / totalAccesses) * mPenalty);
document.getElementById('resAMAT').innerText = amat.toFixed(3) + " units";
} else {
document.getElementById('resAMAT').innerText = "Insufficient data for AMAT (Provide Hit Time & Penalty)";
}
// Show result container
document.getElementById('cacheResult').style.display = 'block';
}