title: What does "Request to ServiceWorker" operation refer to?
body: <p>I'm writting a progressive webapp and implemented a stale while revalidate strategy to handle some of the requests sent by the application.</p>
  
  <p>Checking the network tab in the devtools, i'm seeing that those requests are correctly marked as served <code>from ServiceWorker</code>. However some of them appeared to be quite long (from 200ms to 500ms), so i checked the timing details and found that most of the time was spent in <code>Request to ServiceWorker</code></p>
  
  <p>This <a href="https://developers.google.com/web/tools/chrome-devtools/network-performance/reference#timing-explanation" rel="nofollow noreferrer">link</a> tells us that <code>Request to ServiceWorker</code> refers to "<code>The request is being sent to the service worker.</code>" But it doesn't tell us much on what is actually occurring during this phase and if there is anything we could do to optimize it.</p>
  
  <p>Searching the web, i didn't found futher details about that (only this previous <a href="https://stackoverflow.com/questions/44106334/long-time-waiting-request-to-service-worker">stackoverflow post</a> describing a similar issue).</p>
  
  <p>Does someone have any details on what is actually going on during this <code>Request to ServiceWorker</code> phase ?</p>