Re: "ls -l": Avoid unnecessary getxattr() overhead

[Sven Breuner]

Jim Meyering wrote on 02/09/2012 03:17 PM:
> Pádraig Brady wrote:
> > On 02/09/2012 11:32 AM, Jim Meyering wrote:
> > > Technically, we could probably exempt all files on that device, but
> > > ...
> >
> > So you avoid symlinks as they can point outside the device.
> > Unfortunately so can bind mounts, so you probably have to key on device?
>
> Thanks.  That confirms my impression that my patch was not worthwhile:
> It was buggy, too.
>
> I suppose we could use a little hash table, whose entries are
> <dev_t device_number, bool getfilecon_required>  pairs.
>
> Or even a single static dev_t selinux_challenged_device,
> that if equal to f->stat.st_dev, we can skip the *getfilecon call.
> That should be good enough for most uses.
>
> Here's that simpler patch:
>
> diff --git a/src/ls.c b/src/ls.c
> index f5cd37a..cb9f834 100644
> [...]


Just tried it out and the difference is very significant, as expected.
(Test case with 61,441 files in a directory.)

Current git version without the patch...

$ time ~/tmp/ls-8.15.34-31eee -l >/dev/null

real    0m31.135s
user    0m0.859s
sys     0m4.276s

$ strace -c ~/tmp/ls-8.15.34-31eee -l >/dev/null
% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
 31.13    0.303648           5     61441           lstat
 30.81    0.300585           5     61441     61441 getxattr
 30.65    0.298937           5     61441           lgetxattr
  7.17    0.069987         933        75           getdents
[...]

Current git version patched...

$ time ~/tmp/ls-8.15.34-31eee_patched -l >/dev/null

real    0m21.254s
user    0m0.565s
sys     0m2.496s

$ strace -c ~/tmp/ls-8.15.34-31eee_patched -l >/dev/null
% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
 45.50    0.313386           5     61441           lstat
 43.63    0.300524           5     61441     61441 getxattr
 10.60    0.072986         973        75           getdents
[...]

Thanks!
Sven