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Some tasks very slow after upgrade from Jessie to Stretch




Greetings.


Recently I cloned & upgraded a (virtual) build system, from Jessie to Stretch,
and some tasks have become so slow that it hurts.


Look at 'git archive' for example, the tar part:


bob@build-stretch:/stuff/git/linux-stable$

time git archive v3.18.95 | perf stat tar xC /usr/src/test

 Performance counter stats for 'tar xC /usr/src/test':

   125849.626176   task-clock (msec)        #   0.945 CPUs utilized
             984   context-switches         #   0.008 K/sec
               3   cpu-migrations           #   0.000 K/sec
             135   page-faults              #   0.001 K/sec
 474,044,657,252   cycles                   #   3.767 GHz
 190,146,876,098   stalled-cycles-frontend  #  40.11% frontend cycles idle
 122,803,944,538   stalled-cycles-backend   #  25.91% backend cycles idle
 511,500,080,424   instructions             #   1.08  insn per cycle
                                            #   0.37  stalled cycles per insn
  93,671,911,207   branches                 # 744.316 M/sec
   2,810,364,901   branch-misses            #   3.00% of all branches

   133.182776679 seconds time elapsed

real    2m13.234s
user    0m4.268s
sys     2m6.748s


bob@build-jessie:/stuff/git/linux-stable$

time git archive v3.18.95 | perf stat tar xC /usr/src/test

 Performance counter stats for 'tar xC /usr/src/test':

     3908.736041   task-clock (msec)        #   0.183 CPUs utilized
          44,396   context-switches         #   0.011 M/sec
             134   cpu-migrations           #   0.034 K/sec
             133   page-faults              #   0.034 K/sec
   9,065,881,286   cycles                   #   2.319 GHz
   7,497,944,714   stalled-cycles-frontend  #  82.71% frontend cycles idle
   6,277,695,339   stalled-cycles-backend   #  69.25% backend cycles idle
   2,987,957,839   instructions             #   0.33  insns per cycle
                                            #   2.51  stalled cycles per insn
     576,836,524   branches                 # 147.576 M/sec
      14,885,342   branch-misses            #   2.58% of all branches

    21.365168109 seconds time elapsed

real    0m21.426s
user    0m4.664s
sys     0m6.164s


A bit slower now, on Stretch.

(and why are the perf numbers vastly different I wonder?)


Same thing for 'rm -rf'ing a kernel build tree, on the Stretch VM
it's multiple times slower - takes approx. two minutes.


KVM, same host, storage is virtio block device in LVM.
Setup has been working flawless for years.
Host is also Debian. Still Wheezy, but for a reason.


I've already

- tried different kernels on host and guest
- switched to ext3 from ext4 on guest (a bit faster, but not much)
- used a local git repo in guest (vs. network share which is default)
- asked the Googol

but no remedies yet.



What am I missing?

Has anyone experienced similar things after
upgrading from Jessie to Stretch?



Regards
Ingmar

--
assembled from 100% recycled electrons