Re: dcache_rcu [performance results]

[Dipankar Sarma <dipankar@gamebox.net>]

On Sat, Nov 02, 2002 at 11:08:44AM +0100, Andi Kleen wrote:
> Dipankar Sarma <woofwoof@hathway.com> writes:
> > 
> > I should add that this is a general trend we see in all workloads
> > that do a lot of open/closes and so much so that performance is very
> > sensitive to how close to / your application's working directory
> > is. You would get much better system time if you compile a kernel
> > in /linux as compared to say /home/fs01/users/akpm/kernel/linux ;-)
> 
> That's interesting. Perhaps it would make sense to have a fast path
> that just does a string match of the to be looked up path to a cached copy 
> of cwd and if it matches works as if cwd was the root. Would need to be 
> careful with chroot where cwd could be outside the root and clear the
> cached copy in this case. Then you could avoid all the locking overhead
> for directories above your cwd if you stay in there.

Well, on second thoughts I can't see why the path length for pwd
would make difference for kernel compilation - it uses relative
path and for path lookup, if the first character is not '/', then
lookup is done relative to current->fs->pwd. I will do some more
benchmarking on and verify.

I did get inputs from Troy Wilson who does specweb measurements
that the path name length of the location of the served files
make a difference. I presume his webserver setup used full path names.

Thanks
Dipankar