Work

[Nick Krause]

On Fri, Jul 25, 2014 at 7:35 PM,  <Valdis.Kletnieks at vt.edu> wrote:
> On Fri, 25 Jul 2014 15:23:42 -0700, Arlie Stephens said:
>
>> If you want an annoying problem, explain and/or fix directory
>> performance on ext4. I've got a server where an ls of a directory took
>> 5 seconds, according to "time", even though it only has 295 entries at
>> present.
>
> I don't suppose you could get a trace of where that ls is spending its
> time with the kernel's trace facilities, or even just getting a stack trace
> of where that ls is in the kernel?
>
> I'll go out on a limb and ask if a *second* ls of the same directory runs
> quickly because it's now cache-hot.  If so, I'd start looking at whether
> there's large amounts of *other* disk activity going on, and the reads of the
> directory are getting hung in the I/O queue behind other disk read/writes.
>
> Also, are you doing an 'ls' (which just requires reading the name/inode#
> pairs), or an 'ls -l' whihc in addition requires a stat() call to read in the
> inode itself)?  That makes a lot of difference.  Cache-cold on my laptop, and a
> *huge* Mail/linux-kernel directory (yes, it really *is* an 11M directory,
> it's got a half-million entries in it):
>
> [~] echo 3 >| /proc/sys/vm/drop_caches
> [~] cd Mail
> [~/Mail] time ls linux-kernel/ | wc -l
> 478401
>
> real    0m2.387s
> user    0m0.500s
> sys     0m0.433s
> [~/Mail] ls -ld linux-kernel/
> drwxr-xr-x. 2 valdis valdis 11005952 Jul 25 19:30 linux-kernel/
> [~/Mail] time ls -l linux-kernel/ | wc -l
> 478402
>
> real    0m32.915s
> user    0m2.483s
> sys     0m20.787s
>


Would you find reading strace as I can get the system calls and
profiling the code so
so we can trace where the issue is based on timing and cpu usage of
the code running ?
If not seems the issue is either with I/O queueneeds to add support
for better reading of
multiple large disk actives.
Cheers Nick