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slightlylate's profile
Alex Russell
Alex Russell
Alex Russell
@slightlylate

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Alex Russell

@slightlylate

Chrome Project 🐡 & Web Standards TL; Blink API OWNER Named PWAs w/ @phae; probably making her ☕ DMs open. Tweets my own; press@google.com for official comms.

San Francisco, The Internet
infrequently.org
Joined December 2010

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    1. Alex Russell‏ @slightlylate 16 Oct 2017
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      So you don't; you sell core counts.

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    2. Alex Russell‏ @slightlylate 16 Oct 2017
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      ...and core counts are a lie. DVFS keeps most cores are spun down most of the time. I go into it a tiny bit here:https://www.youtube.com/watch?v=4bZvq3nodf4 …

      2 replies 1 retweet 7 likes
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    3. Alex Russell‏ @slightlylate 16 Oct 2017
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      But it's really hard to overstate the impact of code and data locality. A bigger cache means you go to main memory less.

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    4. Alex Russell‏ @slightlylate 16 Oct 2017
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      Check out the chart here for context: https://www.anandtech.com/show/9837/snapdragon-820-preview/2 …

      1 reply 0 retweets 1 like
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    5. Alex Russell‏ @slightlylate 16 Oct 2017
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      You *badly* want to be in that low/left end of the curve. The easiest way to get that is a bigger cache so more programs do more of the time

      1 reply 0 retweets 1 like
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    6. Alex Russell‏ @slightlylate 16 Oct 2017
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      ...yet, mostly for cost and marketing reasons, nearly all Android-ecosystem SoCs are CPU poor. Many have tiny L2 and little (if any) L3.

      1 reply 1 retweet 2 likes
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    7. Alex Russell‏ @slightlylate 16 Oct 2017
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      MEANWHILE IN CUPERTINO: https://en.wikipedia.org/wiki/Apple_A9  https://en.wikipedia.org/wiki/Apple_A10  https://en.wikipedia.org/wiki/Apple_A11 

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    8. Alex Russell‏ @slightlylate 16 Oct 2017
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      Yes, you're reading that right: between the A10 and the A11, Apple went from 3MB L2/4MB L3 to *8MB L2*

      1 reply 2 retweets 6 likes
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    9. Alex Russell‏ @slightlylate 16 Oct 2017
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      For a sense of scale: http://norvig.com/21-days.html#answers … https://people.eecs.berkeley.edu/~rcs/research/interactive_latency.html …

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    10. Alex Russell‏ @slightlylate 16 Oct 2017
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      So back to our $100 phone. The slow-clocked (1.3Ghz) A53 cores are missing _any_ discernible cache. What does that mean?

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      Alex Russell‏ @slightlylate 16 Oct 2017
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      It means that anything that isn't a tight loop on a small amount of data is going to suffer a main-memory read.

      12:57 PM - 16 Oct 2017
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        2. Alex Russell‏ @slightlylate 16 Oct 2017
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          ...and main-memory reads are 200x more expensive than local (L1) reads. Need that data to keep doing work? Tough luck.

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        3. Alex Russell‏ @slightlylate 16 Oct 2017
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          These situations are called "stalls" or "waits"; CPU is spun up, but it's not retiring instructions (doing work): https://en.wikipedia.org/wiki/Wait_state 

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        4. Alex Russell‏ @slightlylate 16 Oct 2017
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          ...which means that one of the worst effects of the cores-not-caches tradeoff in this phone is that it loses *power efficiency* too.

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        5. Alex Russell‏ @slightlylate 16 Oct 2017
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          The best trade in mobile CPU design today is to swap caches for cores (looking at you @qualcomm, @SamsungSemiUS, & @MediaTek)

          2 replies 0 retweets 7 likes
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        6. Alex Russell‏ @slightlylate 16 Oct 2017
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          So how slow is the @MediaTek MT6737? Lets go to the film! Here are some devices built with this chip:https://www.kimovil.com/en/list-smartphones-by-processor/mediatek-mt6737 …

          2 replies 0 retweets 3 likes
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        7. Alex Russell‏ @slightlylate 16 Oct 2017
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          ...and they all score like this: https://browser.geekbench.com/v4/cpu/4478849 

          2 replies 0 retweets 1 like
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        8. Alex Russell‏ @slightlylate 16 Oct 2017
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          This is 8-9x slower than the iPhone 8: https://browser.geekbench.com/ios_devices/51 

          2 replies 0 retweets 6 likes
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        9. Alex Russell‏ @slightlylate 16 Oct 2017
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          These are both devices you can buy new, today.

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        10. End of conversation

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