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MacOS Catalina: Slow by Design?

(sigpipe.macromates.com)
2031 points jrk | 1 comments | 22 May 20 15:39 UTC | HN request time: 0s | source
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jwlake ◴[22 May 20 16:07 UTC] No.23273573[source]▶
The funny thing is its not transitive. No slowdown if you invoke bash specifically with a new shell.

% rm /tmp/test.sh ; echo $'#!/bin/sh\necho Hello' > /tmp/test.sh && chmod a+x /tmp/test.sh

% time bash /tmp/test.sh && time bash /tmp/test.sh

Hello

bash /tmp/test.sh 0.00s user 0.00s system 83% cpu 0.004 total

Hello

bash /tmp/test.sh 0.00s user 0.00s system 77% cpu 0.003 total

vs the one from the article:

% rm /tmp/test.sh ; echo $'#!/bin/sh\necho Hello' > /tmp/test.sh && chmod a+x /tmp/test.sh

% time /tmp/test.sh && time /tmp/test.sh

Hello

/tmp/test.sh 0.00s user 0.00s system 2% cpu 0.134 total

Hello

/tmp/test.sh 0.00s user 0.00s system 73% cpu 0.004 total

(edited for formating)

replies(3): >>23274970 #>>23275745 #>>23278988 #
1. saurik ◴[23 May 20 01:28 UTC] No.23278988[source]▶
When you run "bash hello" you are calling exec() on bash, passing "hello" as an argument, which bash then reads; when you run "./hello" you are calling exec() on hello: the kernel then treats "hello" as an executable, but notes that "hello" starts with "#!" and then will run the specified interpreter for you, passing "./hello" as an argument. The kernel doesn't think of "hello" as a program when you run "bash hello".