Performance issues with /gnu/store in virtual machines

[Christopher Baines]

Hey,

So I was trying out using VMs created through Guix for more things,
particularly as they can be run as part of derivations, e.g. the system
tests for Guix.

However, I'm seeing anything that does I/O performing very poorly
compared with the host system. See the system call profiles from strace
below, for the following command:

  strace -c find /gnu/store/*-guile* -name guile | wc -l

Is anyone else having difficulties with this, or have any experience
with performance tuning for the software in use here?

Thanks,

Chris



On the host system, I see the following performance:

% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
 76.23    0.001286           0     31978           fcntl
 10.20    0.000172           0      6974           getdents
  7.53    0.000127           0     18673           newfstatat
  3.32    0.000056           0     14208           close
  1.60    0.000027           0      3872           fstat
  1.13    0.000019           0      3853           openat
  0.00    0.000000           0        20           read
  0.00    0.000000           0         4           write
  0.00    0.000000           0        69        50 open
  0.00    0.000000           0         6         6 stat
  0.00    0.000000           0        21           mmap
  0.00    0.000000           0         8           mprotect
  0.00    0.000000           0        33           brk
  0.00    0.000000           0         2         1 ioctl
  0.00    0.000000           0         1         1 access
  0.00    0.000000           0         1           execve
  0.00    0.000000           0         1           uname
  0.00    0.000000           0         1           fchdir
  0.00    0.000000           0         1           arch_prctl
------ ----------- ----------- --------- --------- ----------------
100.00    0.001687                 79726        58 total

Within the VM, I see the following performance:

% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
 59.83    0.851601          46     18673           newfstatat
 13.56    0.193014          50      3853           openat
 10.88    0.154935          22      6974           getdents
  7.95    0.113196           8     14208           close
  4.00    0.056956          15      3872           fstat
  3.58    0.050908           2     31978           fcntl
  0.14    0.002051          66        31        12 open
  0.02    0.000232          12        20           read
  0.01    0.000199           7        30           brk
  0.01    0.000107          18         6         6 stat
  0.01    0.000076           4        21           mmap
  0.00    0.000045           6         8           mprotect
  0.00    0.000030           8         4           write
  0.00    0.000018          18         1         1 access
  0.00    0.000006           3         2         1 ioctl
  0.00    0.000004           4         1           execve
  0.00    0.000003           3         1           uname
  0.00    0.000003           3         1           fchdir
  0.00    0.000001           1         1           arch_prctl
------ ----------- ----------- --------- --------- ----------------
100.00    1.423385                 79685        20 total

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