Bheve: Slow linux syscalls on AMD

[Nils Beyer]

Hi Willem,

Willem Jan Withagen wrote:
> 1) I'm looking for a better basic syscall in Linux that is not cache,
> faked or otherwise tweaked to nog give what I want.
> Would really be nice if there was a NOP_syscall, just go in and out of
> kernel space.....

Hmm, I've tried your test with "getuid". Seems not to be cached. Here's the
diff:

===============================================================================
# diff 0.orig.c 0.c
24c24
<      j=getpid();
---
>      (void)getuid();
38c38
<    printf("Average time for System call getpid : %f\n",avgTimeSysCall);
---
>    printf("Average time for System call getuid : %f\n",avgTimeSysCall);
===============================================================================


And here is the result:

===============================================================================
# strace -c ./0
Average time for System call getuid : 10564.581055
Average time for Function call : 2.285000
% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
100.00    0.004590           0   1000000           getuid
  0.00    0.000000           0         1           read
  0.00    0.000000           0         2           write
  0.00    0.000000           0         2           open
  0.00    0.000000           0         2           close
  0.00    0.000000           0         3           fstat
  0.00    0.000000           0         9           mmap
  0.00    0.000000           0         3           mprotect
  0.00    0.000000           0         1           munmap
  0.00    0.000000           0         1           brk
  0.00    0.000000           0         1         1 access
  0.00    0.000000           0         1           execve
  0.00    0.000000           0         1           arch_prctl
------ ----------- ----------- --------- --------- ----------------
100.00    0.004590               1000027         1 total
===============================================================================



> 3) Can somebody do the same test on an intel plaform and see what the
> results are.

Here is the result from a bhyved CentOS on an Intel i3:

===============================================================================
# strace -c ./0.orig
Average time for System call getpid : 3.776000
Average time for Function call : 2.326000
% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
  -nan    0.000000           0         1           read
  -nan    0.000000           0         2           write
  -nan    0.000000           0         2           open
  -nan    0.000000           0         2           close
  -nan    0.000000           0         3           fstat
  -nan    0.000000           0         9           mmap
  -nan    0.000000           0         3           mprotect
  -nan    0.000000           0         1           munmap
  -nan    0.000000           0         1           brk
  -nan    0.000000           0         1         1 access
  -nan    0.000000           0         1           getpid
  -nan    0.000000           0         1           execve
  -nan    0.000000           0         1           arch_prctl
------ ----------- ----------- --------- --------- ----------------
100.00    0.000000                    28         1 total
===============================================================================




Regards,
Nils