From: linux@horizon.com
Date: Sun, 10 Sep 2006 19:03:32 GMT
Subject: Re: Change set based shallow clone
Message-ID: <20060910190332.17667.qmail@science.horizon.com>
In-Reply-To: <9e4733910609101100u515ae6e3seababd5780db715d@mail.gmail.com>

> Maybe we are looking at the wrong thing, it may be fast to fork a
> process, is it fast for the process to exit?

The lmbench benchmark figures I cited are for fork+exit.  The other is
fork+exec+exit.

> At the time this was measured parsecvs was executing millions of git
> command using system(command). 40% of the CPU was in the kernel, it
> stayed that way for hours.

Ah!  You are aware, aren't you, that system(string) invokes
/bin/sh to parse the string, right?  So you're starting bash
several million times.  ("man system" explains.)

A direct fork() (or even faster, vfork) and exec() is going to have a
lot less overhead, although it's more work to code.  See Stevens for
excellent examples.