Re: [PATCH 4/3] Avoid using 'lstat()' to figure out directories

From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Jul 10, 2009, 00:13 UTC
Message-ID: <alpine.LFD.2.01.0907091658210.3352@localhost.localdomain>
In-Reply-To: <alpine.LFD.2.01.0907091647400.3352@localhost.localdomain>

On Thu, 9 Jul 2009, Linus Torvalds wrote:

Show 5 quoted lines

> 
> So we'd need to do the whole "copy name and add '/' at the end" thing. But 
> the upside would then be that after that, we'd not need any looping to 
> find the right ce. So it might be the right thing to do despite the 
> extra copy.

Naah. I did the numbers. For any normal repository, the 'loop' is going to hit exactly once. Trying to be smarter about the initial binary search isn't going to help, and copying the pathname around is only going to hurt.

In the Linux repo, there's a small handful of cases like this, eg

 - "arch/x86/vdso32"
	arch/x86/vdso/vdso32-setup.c
	arch/x86/vdso/vdso32.S
	arch/x86/vdso/vdsp32/
 - "drivers/scsi/megaraid"
	drivers/scsi/megaraid.c
	drivers/scsi/megaraid.h
	drivers/scsi/megaraid/
 - "include/linux/i2c"
	include/linux/i2c-algo-bit.h
	include/linux/i2c-algo-pca.h
	include/linux/i2c-algo-pcf.h
	include/linux/i2c-dev.h
	include/linux/i2c-gpio.h
	include/linux/i2c-id.h
	include/linux/i2c-ocores.h
	include/linux/i2c-pca-platform.h
	include/linux/i2c-pnx.h
	include/linux/i2c-pxa.h
	include/linux/i2c.h
	include/linux/i2c/

etc (for a total of 45 cases in the whole kernel, if I did my script right), where we'd loop a few times. But we'd spend more effort trying to avoid looping than we spend now on the loop.

		Linus