128 core CPUs are irrelevant, start getting used to things not getting faster? Wrong answer! [LWN.net]

128 core CPUs are irrelevant, start getting used to things not getting faster? Wrong answer!

Posted Apr 28, 2008 7:29 UTC (Mon) by ekj (subscriber, #1524)
In reply to: 128 core CPUs are irrelevant, start getting used to things not getting faster? Wrong answer! by drag
Parent article: Interview with Donald Knuth (InformIT)

But the interesting question isn't what percentage of -all- loads can be paralellized. The interesting question is what percentage of the loads that MATTER can be parallellized.

The loads that -matter- are those where you would like to do more, but are limited by CPU. Or where you'd like to do what you do today quicker.

Offcourse in principle you -always- want to go quicker, but if "ls" already spends 0.042s waiting for I/O and 0.002s doing CPU-work, then it really is of no practical importance if those 0.002s could be efficiently 128-way parallellized.

I think that -most- loads that matter can be parallellized easily. In some cases TRIVIALLY. Can you give a few examples of real-world cases where waiting for the CPU is a real concern, but the problem is not parallellizable ?

I know that the things where I spend time waiting for my CPU are easily parallellizable:

Transcode a movie
Encrypt/decrypt large amounts of data.
Pack/unpack images (PNG, JPG, Raw)
FLAC/Ogg-code wav-files
Graphic performance, particularily 3D.

But really, mostly when I'm waiting for my computer, I'm waiting for it to do IO. Not waiting for it to compute. Thus advances in IO, such as seek-less solid-state disc and faster internet-links are much more relevant to me than faster CPUs. I suspect this is true for most peronal computer-users.

The lightspeed-limit bites for IO too offcourse, particularily the type where I'm doing IO off some device in Australia.

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