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From: Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: Suggested method for returning a string from a C program?
Date: Fri, 28 Mar 2025 16:53:18 -0700
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bart <bc@freeuk.com> writes:
> On 28/03/2025 22:33, Keith Thompson wrote:
>> bart <bc@freeuk.com> writes:
>>> On 28/03/2025 20:41, Scott Lurndal wrote:
>> [...]
>>>> The gnu compiler is not multithreaded.  The single thread was
>>>> compute bound for 13 minutes and 46 seconds.
>>>
>>> So what was that -j96 about?
>> "-j96" is an option to GNU make, not to the compiler.  It might
>> invoke
>> gcc multiple times in parallel, but each invocation of gcc will still be
>> single-threaded.
>
> So, is there just once instance of gcc at work during those 13
> minutes, or multiple?
>
> In other words, would it take longer than 13:40 mins without it, or
> does it help? If -j96 makes no difference, then why specify it?

I haven't done any measurements, but I don't know what's unclear.

If a single thread was compute bound for 13:46, using "-j96"
won't make that single thread run any faster, but it can enable
"make" to do other things while that single thread is running.
It's also common to use "-j" without an argument, to run as many
jobs simultaneously as possible, or "-j$(nproc)" to run as many
parallel jobs as the number of processing units available (if you
have the "nproc" command; it's part of GNU coreutils).

I can imagine "-j" causing problems if dependencies are expressed
incorrectly, but I haven't run into such a problem myself.

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
void Void(void) { Void(); } /* The recursive call of the void */