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Re: kernel compile time

To: Rajagopal Ananthanarayanan <ananth@xxxxxxx>
Subject: Re: kernel compile time
From: Thomas Duffy <tduffy@xxxxxxxxxxxxxxxxxx>
Date: Thu, 1 Jun 2000 11:11:32 -0700 (PDT)
Cc: Kanoj Sarcar <kanoj@xxxxxxxxxxxxxxxxxxx>, linux-origin@xxxxxxxxxxx, skunx@xxxxxxxxxxxxxxxxxxxx
In-reply-to: <39369F00.A9F2279A@xxxxxxx>
Sender: owner-linux-origin@xxxxxxxxxxx
Question:  is this using -j4 MAKE="make -j4" so that it will spawn 4
proccesses for every subdir?  I have found that doing this yeilds about
60 compile proccesses on average during the build.

On Thu, 1 Jun 2000, Rajagopal Ananthanarayanan wrote:

> Going to -j4, elapsed time went from 808sec -> 254sec (4:14)
> which is a scaling of ~3.2 times ... if -j4 had had an
> elapsed time of 202sec (3:22) then it would have been perfect
> scaling. But add in the fact that -j4 vs. NO-J would introduce
> additional complexity in the make itself, which now spawns
> more processes, etc. ... this shows in the increased system time
> for -j4; of course the extra system time also counts increased
> lock contention. For this particular workload (primarily user-mode,
> little-or-no-shared parallelism), -j4 did pretty good.
> 
> Finally, -j6 & -j8 may not discover any extra parallelism
> in the makes ... one gross way to check this is to watch "top"
> and see how many "cc" processes are running on an average.
> If it stays at 4, then -j4 is all that'll work.


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