"As noted in the performance figures in the next section our LISP code is more than twice as slow as the comparable C code."
I don't doubt that you can write productive systems in CL (bit of a fan myself), but the "oh we have smart compilers that just make it as fast as C" just isn't true.
But 50% of C is great. Imagine in Lisp you can achieve 50% performance of C. That means you can write large amounts of your code in Lisp, without the need to use C.
Actually it is both better and worse. One can achieve better than 50% and in many cases one is slower than 50% of C. For example you can optimize your code at runtime using the Lisp compiler. But in many cases you will be slower, since C compilers and libraries tend to have better support for hardware.
For many many applications 50% performance of C is completely sufficient. Zillions of lines of code are written in much slower environments...
And yeah, the expressiveness/speed ratio of Lisp is great.
Starting in the 80s a lot of people/companies made Lisp run with 'acceptable speed' on more conventional Personal Computers, once these got available.
You know what they say, the right tool for the right job.
But 50% (2x) was the lower bound of the slowdown, it was at least twice as slow (from that article), and in the Turing Award lecture Stonebraker mentions an order of magnitude.
Once again, I agree with most of your points, I just think the "we have magical compilers that make the overhead go away" (paraphrasing) is a bit too glib.
That thing ran on a 5 MIPS (Millions instructions per second) 40 bit processor with 40 MB RAM in the end 80s / early 90s.
Suddenly with 1000 times more CPU speed, multi-core machines, fast GPUs, GBs of RAM, etc. it should not be possible to do that anymore?
Because suddenly Lisp is too slow? Why was it fast enough to run that stuff in the 80s on tiny machines?
Naughty Dog wrote Crash Bandicoot for the Playstation using a Common Lisp IDE and a specialized Scheme runtime for the Playstation. It sold millions of games and critics liked it for its fluid gameplay.
Suddenly with machines much faster than the first Playstation this should no longer be possible?
Lisp Machines were invented precisely because Lisp was slow on common hardware, hence the 8 extra tag bits. Lisp Machines are specialized Lisp hardware.
Still that was not the question. The question was why 1000 times faster computers with much more space should not be able to run Lisp applications when in the 70s it was possible to run a whole OS on tiny machines.
Actually Lisp runtimes perform not worse than the JVM.
If you take any fast C program and add all the logic that is missing to make it robust and secure, and refactor it so that it is halfway nimble against changing requirements, it's no longer running at the mythical speed of C.