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Extreme JavaScript Performance
 

Extreme JavaScript Performance

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Talk given at http://jsconf.eu 2009. ...

Talk given at http://jsconf.eu 2009.

You serve up your code gzipped. Your caches are properly configured. Your data (and scripts) are loaded on-demand. That's awesome—so don't stop there. Runtime is another source of slowdowns, and you can learn to conquer those, too.

Learn how to benchmark your code to isolate performance issues, and what to do when you find them. The techniques you'll learn range from the normal (function inlining) to the extreme (unrolling loops).

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    Extreme JavaScript Performance Extreme JavaScript Performance Presentation Transcript

    • Thomas Fuchs @thomasfuchs Extreme JavaScript Performance
    • DO NOT, EVER, OPTIMIZE PREMATURELY
    • http://tr.im/extremejs
    • SpiderMonkey
    • SpiderMonkey JavaScriptCore
    • SpiderMonkey JavaScriptCore JScript
    • SpiderMonkey JavaScriptCore JScript V8
    • #1 avoid function calls
    • function  methodCall(){    function  square(n){  return  n*n  };    var  i=10000,  sum  =  0;    while(i-­‐-­‐)  sum  +=  square(i); } function  inlinedMethod(){      var  i=10000,  sum  =  0;    while(i-­‐-­‐)  sum  +=  i*i; }
    • function  methodCall(){    function  square(n){  return  n*n  };    var  i=10000,  sum  =  0;    while(i-­‐-­‐)  sum  +=  square(i); } function  inlinedMethod(){      var  i=10000,  sum  =  0;    while(i-­‐-­‐)  sum  +=  i*i; }
    • function  methodCall(){    function  square(n){  return  n*n  };    var  i=10000,  sum  =  0;    while(i-­‐-­‐)  sum  +=  square(i); } function  inlinedMethod(){      var  i=10000,  sum  =  0;    while(i-­‐-­‐)  sum  +=  i*i; }
    • methodCall() inlinedMethod() 0.410s 0.150s 0.056s 0.045s uhm,  hmm† 0.128s 0.027s 0.016s
    • methodCall() inlinedMethod() 0.410s 0.150s 0.056s 0.045s uhm,  hmm† 0.128s 0.027s 0.016s
    • methodCall() inlinedMethod() 0.410s 0.150s 0.056s 0.045s uhm,  hmm† 0.128s 0.027s 0.016s
    • methodCall() inlinedMethod() 0.410s 0.150s 0.056s 0.045s uhm,  hmm† 0.128s 0.027s 0.016s
    • methodCall() inlinedMethod() 0.410s 0.150s 0.056s 0.045s uhm,  hmm† 0.128s 0.027s 0.016s
    • IE8 throws this warning after 1 second
    • #2 embrace the language
    • function  literals(){    var  a  =  [],  o  =  {}; } function  classic(){    var  a  =  new  Array,  o  =  new  Object; }
    • classic() literals() 0.291s 0.265s 0.020s 0.016s 0.220s 0.185s 0.024s 0.010s
    • classic() literals() 0.291s 0.265s 0.020s 0.016s 0.220s 0.185s 0.024s 0.010s
    • classic() literals() 0.291s 0.265s 0.020s 0.016s 0.220s 0.185s 0.024s 0.010s
    • classic() literals() 0.291s 0.265s 0.020s 0.016s 0.220s 0.185s 0.024s 0.010s
    • classic() literals() 0.291s 0.265s 0.020s 0.016s 0.220s 0.185s 0.024s 0.010s
    • >  parseInt(12.5); 12
    • >  ~~(1  *  "12.5") 12
    • double bitwise NOT* floors the number >  ~~(1  *  "12.5") 12 1 * string coerces the string into a float, result = 12.5 *good overview on http://tr.im/bitwise
    • parseInt() weird  stuff 0.003s 0.002s 0.088s 0.081s uhm,  hmm† 0.547s 0.109s 0.282s
    • parseInt() weird  stuff 0.003s 0.002s 0.088s 0.081s uhm,  hmm† 0.547s 0.109s 0.282s
    • parseInt() weird  stuff 0.003s 0.002s 0.088s 0.081s uhm,  hmm† 0.547s 0.109s 0.282s
    • parseInt() weird  stuff 0.003s 0.002s 0.088s 0.081s uhm,  hmm† 0.547s 0.109s 0.282s
    • parseInt() weird  stuff 0.003s 0.002s 0.088s 0.081s uhm,  hmm† 0.547s 0.109s 0.282s
    • Firefox is 30x faster than Safari parseInt() weird  stuff 0.003s 0.002s 0.088s 0.081s uhm,  hmm† 0.547s 0.109s 0.282s
    • #3 loops
    • var  test  =  ''; for  (var  i  =  0;i<10000;i++)  test  =  test  +  str; var  test  =  '',  i  =  10000; while(i-­‐-­‐)  test  =  test  +  str;
    • for  loop while  loop 0.12s 0.12s 0.13s 0.13s 0.6s 0.6s 0.04s 0.04s
    • for  loop while  loop 0.12s 0.12s 0.13s 0.13s 0.6s 0.6s 0.04s 0.04s
    • for  loop while  loop 0.12s 0.12s 0.13s 0.13s 0.6s 0.6s 0.04s 0.04s
    • for  loop while  loop 0.12s 0.12s 0.13s 0.13s 0.6s 0.6s 0.04s 0.04s
    • for  loop while  loop 0.12s 0.12s 0.13s 0.13s 0.6s 0.6s 0.04s 0.04s
    • 3 expressions in “for” var  test  =  ''; for  (var  i  =  0;i<10000;i++)  test  =  test  +  str; var  test  =  '',  i  =  10000; while(i-­‐-­‐)  test  =  test  +  str; 1 expression in “while” (when i equals 0, expression will be false)
    • function  normalLoop(){    var  i=60,  j=0;    while(i-­‐-­‐)  j++; }
    • function  unrolledLoop(){    var  j=0;    j++;  j++;  j++;  j++;  j++;  j++;      j++;  j++;  j++;  j++;  j++;  j++;    j++;  j++;  j++;  j++;  j++;  j++;    j++;  j++;  j++;  j++;  j++;  j++;    j++;  j++;  j++;  j++;  j++;  j++;    j++;  j++;  j++;  j++;  j++;  j++;    j++;  j++;  j++;  j++;  j++;  j++;    j++;  j++;  j++;  j++;  j++;  j++;    j++;  j++;  j++;  j++;  j++;  j++;    j++;  j++;  j++;  j++;  j++;  j++; }
    • normalLoop() unrolledLoop() 0.023s 0.010s 0.003s 0.001s 0.032s 0.015s 0.005s 0.001s
    • normalLoop() unrolledLoop() 0.023s 0.010s 0.003s 0.001s 0.032s 0.015s 0.005s 0.001s
    • normalLoop() unrolledLoop() 0.023s 0.010s 0.003s 0.001s 0.032s 0.015s 0.005s 0.001s
    • normalLoop() unrolledLoop() 0.023s 0.010s 0.003s 0.001s 0.032s 0.015s 0.005s 0.001s
    • normalLoop() unrolledLoop() 0.023s 0.010s 0.003s 0.001s 0.032s 0.015s 0.005s 0.001s
    • #4 cache globals
    • function  uncached(){    var  i  =  10000;    while(i-­‐-­‐)  window.test  =  'test'; } function  cached(){    var  w  =  window,  i  =  10000;    while(i-­‐-­‐)  w.test  =  'test'; }
    • uncached cached 1.440s 0.825s 0.07s 0.07s 2.22s 2.19s 0.48s 0.16s
    • uncached cached 1.440s 0.825s 0.07s 0.07s 2.22s 2.19s 0.48s 0.16s
    • uncached cached 1.440s 0.825s 0.07s 0.07s 2.22s 2.19s 0.48s 0.16s
    • uncached cached 1.440s 0.825s 0.07s 0.07s 2.22s 2.19s 0.48s 0.16s
    • uncached cached 1.440s 0.825s 0.07s 0.07s 2.22s 2.19s 0.48s 0.16s
    • Safari is 20x faster than Firefox uncached cached 1.440s 0.825s 0.07s 0.07s 2.22s 2.19s 0.48s 0.16s
    • uncached cached 1.440s 0.825s 0.07s 0.07s 2.22s 2.19s 0.48s 0.16s Now IE works with >1s durations. WTF?
    • #5 expression tuning
    • var  b  =  false,  n  =  99; function(){    return  n*n  &&  b; } function(){    return  b  &&  n*n; }
    • var  b  =  false,  n  =  99; function(){    return  n*n  &&  b; } function(){    return  b  &&  n*n; } b is false, so n*n doesn’t need to get evaluated
    • not  tuned tuned 0.005s 0.004s 0.011s 0.010s 0.906s 0.391s 0.037s 0.021s
    • not  tuned tuned 0.005s 0.004s 0.011s 0.010s 0.906s 0.391s 0.037s 0.021s
    • not  tuned tuned 0.005s 0.004s 0.011s 0.010s 0.906s 0.391s 0.037s 0.021s
    • not  tuned tuned 0.005s 0.004s 0.011s 0.010s 0.906s 0.391s 0.037s 0.021s
    • not  tuned tuned 0.005s 0.004s 0.011s 0.010s 0.906s 0.391s 0.037s 0.021s
    • not a pure engine optimization, the execution actually stops here, n=2 needs to be evaluated, >>>  var  n  =  1; so n is set to 2 undefined >>>  if(true  &&  (n=2))  ...; >>>  n 2 >>>  if(true  ||  (n=3))  ...; >>>  n here it doesn’t 2 (expression must be true), so n is NOT set to 3
    • #6 what not to use
    • function(){    var  obj  =  {  prop:  'test',  str:  ''  };    with(obj){          var  i  =  10000;        while(i-­‐-­‐)  str  +=  prop;        return  str;    } } function(){    var  obj  =  {  prop:  'test',  str:  ''  },  i  =  10000;    while(i-­‐-­‐)  obj.str  +=  obj.prop;    return  obj.str; }
    • with(obj){  p  } obj.p 0.071s 0.012s 0.039s 0.028s 0.078s 0.078s 0.077s 0.006s
    • with(obj){  p  } obj.p 0.071s 0.012s 0.039s 0.028s 0.078s 0.078s 0.077s 0.006s
    • with(obj){  p  } obj.p 0.071s 0.012s 0.039s 0.028s 0.078s 0.078s 0.077s 0.006s
    • with(obj){  p  } obj.p 0.071s 0.012s 0.039s 0.028s 0.078s 0.078s 0.077s 0.006s
    • with(obj){  p  } obj.p 0.071s 0.012s 0.039s 0.028s 0.078s 0.078s 0.077s 0.006s
    • var  a  =  0; function(){    try{        a  +=  1;    }  catch(e)  {} } function(){    a  +=  1; }
    • try/catch no  try/catch 0.006s 0.005s 0.287s 0.011s 0.460s 0.460s 0.123s 0.012s
    • try/catch no  try/catch 0.006s 0.005s 0.287s 0.011s 0.460s 0.460s 0.123s 0.012s
    • try/catch no  try/catch 0.006s 0.005s 0.287s 0.011s 0.460s 0.460s 0.123s 0.012s
    • try/catch no  try/catch 0.006s 0.005s 0.287s 0.011s 0.460s 0.460s 0.123s 0.012s
    • try/catch no  try/catch 0.006s 0.005s 0.287s 0.011s 0.460s 0.460s 0.123s 0.012s
    • no try/catch try/catch Firefox 3.5 Safari 4.0 Chrome 3 IE 8 0 0,1 0,2 0,3 0,4 0,5
    • no try/catch try/catch Firefox 3.5 Safari 4.0 Chrome 3 IE 8 0 0,1 0,2 0,3 0,4 0,5
    • no try/catch try/catch Firefox 3.5 Safari 4.0 Chrome 3 IE 8 0 0,1 0,2 0,3 0,4 0,5
    • no try/catch try/catch Firefox 3.5 Safari 4.0 Chrome 3 IE 8 0 0,1 0,2 0,3 0,4 0,5
    • no try/catch try/catch Firefox 3.5 Safari 4.0 Chrome 3 IE 8 0 0,1 0,2 0,3 0,4 0,5
    • Modern JavaScript engines have JIT compilers, which don’t support certain features well
    • Avoid stuff that’s not available in ECMA-262 5th Edition “strict” mode, see John’s blog post
    • Avoid stuff that’s not available in ECMA-262 5th Edition “strict” mode, see John’s blog post http://tr.im/ecma262
    • alert((function(){return"alert (("+arguments.callee.toString() .replace(/s/g,"")+")());";})());
    • alert((function(){return"alert (("+arguments.callee.toString() .replace(/s/g,"")+")());";})());
    • (function(){  return  2  *  3;  }).toString();
    • function  ()  {  return  2  *  3;  }
    • function  ()  {  return  2  *  3;  } function  ()  {  return  2  *  3;  }
    • function  ()  {  return  2  *  3;  } function  ()  {  return  2  *  3;  } function  ()  {  return  2  *  3;  }
    • function  ()  {  return  2  *  3;  } function  ()  {  return  2  *  3;  } function  ()  {  return  2  *  3;  } function  ()  {  return  6;  }
    • function  ()  {  return  2  *  3;  } function  ()  {  return  2  *  3;  } function  ()  {  return  2  *  3;  } function  ()  {  return  6;  } WTF?
    • More in http://jsrocks.com
    • More in http://jsrocks.com
    • DO NOT, EVER, OPTIMIZE PREMATURELY
    • Q&A And thanks! http://javascriptrocks.com/ @thomasfuchs on twitter