FrontEnd Performance Beginner to Expert to Crazy Person

Philip Tellis @bluesmoon http://tech.bluesmoon.info http://www.soasta.com/mpulse/

Get the most benefit with the least effort

0 Start with a really slow site

0.1 Start Measuring

Or use RUM for real user data (boomerang/mPulse)

0.2 enable gzip http://www.slideshare.net/billwscott/improving-netflix-performance-experience

You can pre-gzip gzip_static in nginx

0.2 gzip • For dynamic content, use chunked transfers with gzipped chunks • You can do this by flushing buffers on the server

0.3 ImageOptim

0.4 Cache Cache-control: public, max-age=31415926 Do NOT set LastModified or Etags headers

Yes, that was 10 million pies

0 Congratulations You’ve just been promoted!

1 What the Experts do

1.1 CDN Serve your root domain through a CDN

1.1 CDN And make sure your CSS is on the same domain http://www.jonathanklein.net/2014/02/revisiting-cookieless-domain.html

1.1 CDN Google Chrome will open two TCP connections to the primary host, one for the page, and the second "just in case"

1.1 Google Chrome will open two TCP connections to the primary host, one for the page, and the second "just in case"

1.1 Don’t waste it

1.2 Split JavaScript • Critical: in the HEAD • Enhancements: loaded async • Flush buffers after the HEAD • for HTTP/2, these would have different priorities

1.3 Audit your CSS

Also checkout uncss for a command line version (also with a grunt version) https://github.com/giakki/uncss https://github.com/addyosmani/grunt-uncss

1.4 Parallelize downloads… or maybe don’t • You can have more bandwidth, but you cannot have lower latency • Mitigate latency effects by parallelizing across multiple TCP sockets • But with HTTP/2, this rule is turned on its head http://www.soasta.com/blog/more-bandwidth-isnt-a-magic-bullet-for-web-performance/

1.5 Flush Early and Often Get bytes to the client ASAP to: • avoid TCP Slow Start, • speed up CSS • Help the browser’s lookahead parser

1.6 Increase initcwnd Initial Congestion Window: Number of packets to send before waiting for an ACK http://www.cdnplanet.com/blog/tune-tcp-initcwnd-for-optimum-performance/

1.6 Increase initcwnd

1.6 Increase initcwnd @mobtec on Twitter

1.6b Also… net.ipv4.tcp_slow_start_after_idle=0 http://www.lognormal.com/blog/2012/09/27/linux-tcpip-tuning/

1.7 PageSpeed mod_pagespeed and ngx_pagespeed

1.8 Don’t just FastClick • FastClick fires a Click onTouchEnd • It might be better to initiate a TCP connect onTouchStart and fetch content normally onClick • Load a 0 byte image from the domain to do this

1.9 Use UserTiming to measure your code • The UserTiming API allows you to set performance timeline marks within your code • performance.mark(“name”) • performance.measure(“name”, “start_mark”, “end_mark”) http://www.html5rocks.com/en/tutorials/webperformance/usertiming/

Relax

2 You’ve reached crazyland

Sort in ascending order of signal latency • Electrons through copper • Light through fibre • Pulsars • Station Wagons • Smoke Signals

Sort in ascending order of signal latency 1.Pulsars (light through vacuum) 2.Smoke Signals (light through air) 3.Electrons through copper / Light through fibre 4.Station Wagons (possibly highest bandwidth)

2.0 Bandwidth is different around the world

2.0 As are people

2.0 Study real user data Look for potential places to parallelize, predict and cache

2.1 Use RUM to determine optimum POP location • Use RUM to measure latency from user to multiple POPs • Pick POP based on lowest latency • Adapt to changes in network topology http://www.slideshare.net/rmaheshw/velocity-2015-pops-and-rum

2.1 Use RUM to determine best CDN • Use RUM to measure latency from user to multiple CDN providers • Dynamically pick CDN based on what works best

2.2 Pre-load Pre-fetch assets required for the next page in a process flow

2.2b pre-render

2.2b • Does a DNS lookup for hostname mentioned in URL • This could help reduce latency when the request shows up — for first page views at least • Your DNS TTL needs to be long enough to survive past a page load

2.2b • Tells the parser that this resource will be required later on • Browser can start downloading in the background if it has nothing better to do with its resources • Resource needs to have suitable cache headers

2.2b • Tells the parser that this page is likely to be requested by the user • Browser downloads page, and all its resources, renders it, executes JavaScript and fires the onload event. • It’s like opening the page in a hidden Tab

2.2b • When user follows the URL, the page just shows up (< 5ms latency) • This is actually faster than switching tabs in the browser • The onVisibilityChange event fires and visibilityState changes from “prerender” to “visible” or “hidden”

2.2b — Caveats • The page needs to be requested using GET • The page should not require Authentication (401 response) • The calling page should NOT change the state of Cookies after the pre-rendered page has been requested

2.2c onVisibilityChange And while you’re at it, don’t do expensive work if the page is hidden https://developer.mozilla.org/en-US/docs/Web/Guide/User_experience/ Using_the_Page_Visibility_API

2.3 Post-load Fetch optional assets after onload

2.4 Detect broken accept-encoding Many Windows anti-viruses and firewalls disable gzip by munging the Accept-Encoding header http://www.lognormal.com/blog/2012/08/17/accept-encoding-stats/

2.5 HTTP/2 • Only one TCP connection per host • Do NOT use domain sharding • Do NOT use sprites • Do use Stream Multiplexing with Priorities • Do use Server Push http://chimera.labs.oreilly.com/books/1230000000545/ch12.html

— Tim Kadlec “4:2:0 subsampling of JPEGs gets a 62.5% memory savings” 2.6 Use 4:2:0 Chroma Subsampling Chroma Subsampling takes advantage of the fact that the human visual system is less sensitive to changes in colour than luminance http://en.wikipedia.org/wiki/Chroma_subsampling

2.7 Resize Images for target Device Dimensions Resizing Images for specific screen sizes could be the difference between 1.5s and 30ms https://speakerdeck.com/tkadlec/mobile-image-processing-at-velocity-sc-2015

2.8 Don’t force layout operations • DOM manipulations followed by a read of invalidated properties forces a layout • This has a huge CPU impact • Read before write • Batch update • Move operations into the HEAD Amiya Gupta @ Velocity 2015

2.9 Understand 3PoFs Use blackhole.webpagetest.org to test for 3rd party single points of failure http://blog.patrickmeenan.com/2011/10/testing-for-frontend-spof.html

2.9 3PoFs Request Map by Simon Hearne

2.10 Understand the Iframe Loader Technique Take required but non-critical assets out of the critical path http://www.lognormal.com/blog/2012/12/12/the-script-loader-pattern/

2.11 Understand your SpeedIndex http://heatmap.webperf.tools/render/150611_88_af4b9ceaa938f1b4647ff2e8ed41b550/10000

2.12 What does your site cost? http://whatdoesmysitecost.com/test/150611_N5_9495f479626f6589299f62e440724064

2.13 Prioritize optimizations based on user impact Conversion Impact Score in mPulse DSWB

2.14 Become a WebPageTest power user • Check out the comparison view • Collect packet captures • Use Wireshark • Test out different network types

References • WebPageTest — http://webpagetest.org • Boomerang — http://www.lognormal.com/boomerang/doc/ • SOASTA mPulse — http://www.soasta.com/mpulse • Netflix gzip study — http://www.slideshare.net/billwscott/improving-netflix-performance-experience • Nginx gzip_static — http://wiki.nginx.org/HttpGzipStaticModule • ImageOptim — http://imageoptim.com/ • uncss — https://github.com/giakki/uncss • grunt-uncss — https://github.com/addyosmani/grunt-uncss • Caching — http://www.mnot.net/cache_docs/ • Same domain CSS — http://www.jonathanklein.net/2014/02/revisiting-cookieless-domain.html • initcwnd — http://www.cdnplanet.com/blog/tune-tcp-initcwnd-for-optimum-performance/ • Linux TCP Tuning — http://www.lognormal.com/blog/2012/09/27/linux-tcpip-tuning/ • Prerender — https://developers.google.com/chrome/whitepapers/prerender • DNS prefetching — https://developer.mozilla.org/en-US/docs/Controlling_DNS_prefetching • Subresource — http://www.chromium.org/spdy/link-headers-and-server-hint/link-rel-subresource • FE SPoF — http://blog.patrickmeenan.com/2011/10/testing-for-frontend-spof.html • Page Visibility API — https://developer.mozilla.org/en-US/docs/Web/Guide/User_experience/Using_the_Page_Vis... • HTTP/2 — http://chimera.labs.oreilly.com/books/1230000000545/ch12.html • More Bandwidth is not a Magic Bullet — http://performancebeacon.com/more-bandwidth-isnt-a-magic-bullet-for... • The UserTiming API — http://www.html5rocks.com/en/tutorials/webperformance/usertiming/ • The 3.5s dash for attention — http://www.slideshare.net/buddybrewer/the-35s-dash-for-attention-and-other-stuff-we-... • POPs & RUM — http://www.slideshare.net/rmaheshw/velocity-2015-pops-and-rum • Optimizing Images for Mobile — https://speakerdeck.com/tkadlec/mobile-image-processing-at-velocity-sc-2015 • Optimizing the MSN Homepage — Amiya Gupta @ Velocity 2015 • Simon Hearne’s Webperf Tools — http://requestmap.webperf.tools and http://heatmap.webperf.tools • What does my site cost — http://whatdoesmysitecost.com

Thank You

Philip Tellis @bluesmoon http://tech.bluesmoon.info http://www.soasta.com/mpulse/

Image Credits • Apple Pie
 http://www.flickr.com/photos/24609729@N00/3353226142/ • Kittens in a PC
 http://www.flickr.com/photos/43525343@N08/6417971383/