rawhide ext4/virtio FS performance hit (10x slower) ?

[Jim Meyering]

Josh Boyer wrote:

> On Mon, May 7, 2012 at 8:43 AM, Jim Meyering <jim at meyering.net> wrote:
>> Today I noticed that some tests from coreutils' test suite
>> were taking far longer than they used to on rawhide.
>> For example, run this command in an empty directory:
>>
>>  seq 200000|env time xargs touch
>>
>> it takes < 5s on F17 3.3.4-1.fc17.x86_64 ext4/sdb8/SSD, yet
>> it takes 47s on rawhide 3.4.0-0.rc5.git5.1.fc18.x86_64 ext4/vda1/SSD
>>
>> 10x performance hit... ouch.
>>
>> Does anyone know why?
>
> Rawhide has all the kernel debug options turned on.  It isn't
> worthwhile doing a comparison when those are enabled.  You could try
> again with the first -rc6 build that shows up, as that will have the
> options disabled.

Hi Josh,

I've just rerun the test with 3.4.0-0.rc6.git1.1.fc18.x86_64,
and it takes just as long, so the hit is *not* due to debug options:

$ seq 200000|env time xargs touch
0.17user 41.98system 0:48.22elapsed 87%CPU (0avgtext+0avgdata 1424maxresident)k
88inputs+0outputs (0major+4502minor)pagefaults 0swaps