Re: Change set based shallow clone

From: linux@horizon.com <linux@horizon.com>
Date: Sep 10, 2006, 19:03 UTC
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.

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