.. titel: NIC-ringbuffer en IRQ-affiniteitscalculator
.. slak: nic-ring-buffer-calculator
.. datum: 27-03-2026 12:00:00 UTC
.. tags: linux, nic, irq, rss, performance, kernel, rekenmachine, tool
.. categorie: Rekenmachines
.. link:
.. beschrijving: Bereken de aanbevolen ethtool-ringbuffergroottes, het aantal RSS-wachtrijen en de strategie voor het vastzetten van CPU-affiniteit op basis van interfacesnelheid, CPU-aantal en verkeersprofiel.
.. typ: tekst
<style>
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</style>
<div class="calc-container">
<div class="calc-header">
<h2>NIC-ringbuffer en IRQ-affiniteitscalculator</h2>
<p>Berekenen<code style="color:rgba(255,255,255,0.9);background:rgba(0,0,0,0.2);padding:2px 6px;border-radius:3px">ethtool -G</code>ringbuffergroottes, aantal RSS-wachtrijen en CPU-affiniteit/irqbalance-pinningstrategie.</p>
<div class="input-grid">
<div class="input-group">
<label>Interfacesnelheid</label>
<select id="linkSpeed">
<option value="1">1 Gbps</option>
<option selected="" value="10">10 Gbps</option>
<option value="25">25 Gbps</option>
<option value="40">40 Gbps</option>
<option value="100">100 Gbps</option>
</select>
</div>
<div class="input-group">
<label>CPU-kernen beschikbaar</label>
<input id="cpuCount" max="256" min="1" type="number" value="8"/>
</div>
<div class="input-group">
<label>Verkeersprofiel</label>
<select id="trafficProfile">
<option value="bulk">Bulk / streaming (grote frames)</option>
<option selected="" value="rpc">Gemengd / RPC (gevarieerde framegrootte)</option>
<option value="pps">Hoge PPS (kleine frames)</option>
</select>
</div>
<div class="input-group">
<label>Coalescentiedoel onderbreken (μs)</label>
<input id="coalesceUs" max="1000" min="1" type="number" value="50"/>
</div>
<div class="input-group">
<label>Interfacenaam</label>
<input id="ifName" placeholder="eth0" type="text" value="eth0"/>
</div>
</div>
<div class="button-container">
<button class="calc-button" onclick="calcNic()">Berekenen</button>
</div>
</div>
<div id="nicResult" style="display:none"></div>
<div class="result-section">
<div class="section-header">Afweging tussen ringbuffer en droprate</div>
<div class="section-content">
<table>
<tr><th>Ringmaat</th><th>Latentie-impact</th><th>Valrisico</th><th>Gebruikscasus</th></tr>
<tr><td>256</td><td>Zeer laag</td><td>Hoog (burstdalingen)</td><td>Realtime prioriteit met lage latentie</td></tr>
<tr><td>512</td><td>Laag</td><td>Medium</td><td>Latentiegevoelige RPC</td></tr>
<tr><td>1024</td><td>Medium</td><td>Laag</td><td>Algemeen doel</td></tr>
<tr><td>2048</td><td>Middelhoog</td><td>Zeer laag</td><td>Bulkoverdracht, 10Gbps+</td></tr>
<tr><td>4096</td><td>Hoog (voegt latentie toe)</td><td>Minimaal</td><td>100 Gbps, aanhoudende PPS</td></tr>
</table>
</div>
</div>
</div>
<script>
function calcNic() {
    const speedGbps = parseInt(document.getElementById('linkSpeed').value);
    const cpus = parseInt(document.getElementById('cpuCount').value);
    const profile = document.getElementById('trafficProfile').value;
    const coalesceUs = parseInt(document.getElementById('coalesceUs').value);
    const iface = document.getElementById('ifName').value.trim() || 'eth0';
    const div = document.getElementById('nicResult');
    div.style.display = 'block';

    if (isNaN(cpus) || cpus < 1 || isNaN(coalesceUs) || coalesceUs < 1) {
        div.innerHTML = '<div class="result-section"><div class="section-header">Results</div><div class="section-content"><strong style="color:red">Invalid input.</strong></div></div>';
        return;
    }

    // Ring buffer sizing: ceil(link_speed_bps * coalesce_delay_s / (8 * frame_size))
    // Frame size heuristic by profile
    const frameSizes = { bulk: 9000, rpc: 1500, pps: 64 };
    const frameSize = frameSizes[profile];
    const speedBps = speedGbps * 1e9;
    const coalesceS = coalesceUs / 1e6;
    const rawRing = Math.ceil((speedBps * coalesceS) / (8 * frameSize));
    // Round up to nearest power of 2 (common NIC constraint)
    let ringSize = 1;
    while (ringSize < rawRing) ringSize *= 2;
    ringSize = Math.min(ringSize, 4096); // max typical ring size

    // RSS queues: min(cpus, speed-based cap, 64)
    const speedQueues = speedGbps <= 1 ? 4 : speedGbps <= 10 ? 8 : speedGbps <= 25 ? 16 : 32;
    const rssQueues = Math.min(cpus, speedQueues, 64);

    // CPU affinity: prefer first N CPUs, skip CPU 0 if NUMA/irqbalance concern
    const affinityCpus = rssQueues <= 4 ? `1-${rssQueues}` : `0-${rssQueues - 1}`;

    div.innerHTML = `<div class="result-section">
        <div class="section-header">Recommended Settings</div>
        <div class="section-content">
            <div class="metric-grid">
                <div class="metric-card"><div class="metric-value">${ringSize}</div><div class="metric-label">Ring buffer size (RX &amp; TX)</div></div>
                <div class="metric-card"><div class="metric-value">${rssQueues}</div><div class="metric-label">RSS queues</div></div>
                <div class="metric-card"><div class="metric-value">${coalesceUs} μs</div><div class="metric-label">Interrupt coalescing</div></div>
                <div class="metric-card"><div class="metric-value">${speedGbps} Gbps</div><div class="metric-label">Link speed</div></div>
            </div>
            <div class="info-box">
                <strong>Calculation:</strong> ceil(${speedGbps}Gbps &times; ${coalesceUs}μs / (8 &times; ${frameSize}B)) = ${rawRing} &rarr; rounded up to ${ringSize} (power of 2)
            </div>
            <div class="cmd-block"># Set ring buffer (${iface})
ethtool -G ${iface} rx ${ringSize} tx ${ringSize}

# Set RSS queue count
ethtool -L ${iface} combined ${rssQueues}

# Set interrupt coalescing
ethtool -C ${iface} rx-usecs ${coalesceUs} tx-usecs ${coalesceUs}

# Pin IRQs to CPUs ${affinityCpus} (run after ethtool -L)
# Find IRQ numbers: grep ${iface} /proc/interrupts | awk '{print $1}' | tr -d ':'
# Then: echo ${affinityCpus} > /proc/irq/&lt;N&gt;/smp_affinity_list

# Or use irqbalance with policy hint:
IRQBALANCE_ARGS="--policyscript=/etc/irqbalance/policy.sh" systemctl restart irqbalance</div>
            <button class="calc-button" style="margin-top:10px;padding:10px 24px;font-size:14px" onclick="copyBlock()">Copy Commands</button>
        </div>
    </div>`;

    window._lastCmds = `# Set ring buffer (${iface})\nethtool -G ${iface} rx ${ringSize} tx ${ringSize}\n\n# Set RSS queue count\nethtool -L ${iface} combined ${rssQueues}\n\n# Set interrupt coalescing\nethtool -C ${iface} rx-usecs ${coalesceUs} tx-usecs ${coalesceUs}`;
}

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