<p></p>
<p dir="auto">In an attempt to isolate what's going on, I left the load normal and used render_list to render z17 tiles. It started off behaving as above, with 4 seconds per tile rendered and CPU usage <50%. Then without changing anything, throughput spiked up, time/tile went down, and CPU usage went to 100%.</p>
<p dir="auto"><a target="_blank" rel="noopener noreferrer" href="https://user-images.githubusercontent.com/1190866/268131863-a278a4cb-0f60-4828-a30b-126029eac01a.png"><img src="https://user-images.githubusercontent.com/1190866/268131863-a278a4cb-0f60-4828-a30b-126029eac01a.png" alt="image" style="max-width: 100%;"></a></p>
<p dir="auto">render_list was with <code class="notranslate">-n 80</code> and num_threads is 120, and the machine has 80 hardware threads</p>
<p dir="auto">In an effort to reduce the problem down, I shut off apache2/mod_tile and tried render_list with an assortment of -n. Increasing -n doesn't increase throughput or CPU usage, except that sometimes it goes from not running at capacity to generating more tiles and being CPU bottlenecked.</p>
<p dir="auto">I'm wondering, could some kind of lock be limiting how many requests per second it can deal with? But that wouldn't explain the bursts of good performance.</p>

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