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POReasons for high CPU usage in SocketInputStream.socketRead0()
 

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  1. POReasons for high CPU usage in SocketInputStream.socketRead0()
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    <p>While profiling homegrown web-application I came across following very strange (at least for me) observation.</p> <p>Almost all time is spent in <code>socketRead0()</code> method of a <code>SocketInputStream</code> class. It's not surprising because my application do a networking with a remote service on each request. What is strange that not only <em>wall clock time</em> usage is high for this method, <em>CPU clock time</em> also very high. I can't understand why CPU time is high, because if my application wait for remote service to reply (which is not so fast in fact), there is nothing to do left for application itself. So CPU time should be apparently low.</p> <p>Some more observation:</p> <ul> <li>VisualVM in sampling mode shows that method <code>SocketInputStream.socketRead0()</code> is eating up to 95% of time (both wall clock time <strong>and</strong> CPU time);</li> <li><code>mpstat</code> (we use Linux as a OS) shows around ~90% user time and ~1-3% system time (the rest is idle time);</li> <li>application deployed on the dedicated server;</li> <li>remote service is HTTP web-application also. Average response time is about 100ms. Average response size is about 2Kb.</li> <li>my application use spring <code>RestTemplate</code> to interact with remote service, not the <code>SocketInputStream</code> directly.</li> </ul> <p>For now I have only one idea — maybe this is overhead of calling native methods in JVM (<code>SocketInputStream.socketRead0()</code> is native)?</p> <p>What do you think? Is there any other reasons to this?</p>
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    1. USAdam Siemion
    1. USDenis Bazhenov
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    1. COIt seems a bit strange, but not impossible. Can you give more context? Does "homegrown web-application" play with sockets directly? Are you reading single bytes?
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      1. USthemel
    2. COSome more context under "Observations"
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      1. USDenis Bazhenov
    3. CODo you have an idea of what's further up the stack or what the sizes of your reads are? I can imagine reaching your numbers if you e.g. tried to do JSON parsing from an unbuffered socket.
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