[pve-devel] [PATCH qemu] add pve-api-updates trigger

[Thomas Lamprecht]

Am 8/12/19 um 3:21 PM schrieb Dominik Csapak:
> i just benchmarked a cached stat version vs. not cached

Thanks.

> code is the following:
> 
> ----8<----
> use strict;
> use warnings;
> use utf8;
> 
> use Benchmark qw(cmpthese);
> use PVE::Tools qw(run_command);
> 
> my $kvm_cache;
> my $kvm_timestamp;
> 
> sub get_kvm_version {
>     my $kvm_user_version = 'unknown';
> 
>     my $code = sub {
>         my $line = shift;
>         if ($line =~ m/^QEMU( PC)? emulator version (\d+\.\d+(\.\d+)?)(\.\d+)?[,\s]/) {
>             $kvm_user_version = $2;
>         }
>     };
> 
>     eval { run_command("kvm -version", outfunc => $code); };
>     warn $@ if $@;
>     return $kvm_user_version;
> }
> 
> cmpthese(-10, {
>     cache => sub {
>         my $mtime = (stat("/usr/bin/kvm"))[9];
>         if (!$kvm_timestamp || !$kvm_cache || $kvm_timestamp < $mtime) {
>             $kvm_timestamp = $mtime;
>             $kvm_cache = get_kvm_version();
>         }
>         return $kvm_cache;
>     },
>     noncached => sub {
>         return get_kvm_version();
>     }
> });
> ---->8----
> 
> result is:
> 
>               Rate noncached     cache
> noncached   27.9/s        --     -100%
> cache     696192/s  2490994%        -
> 
> so a single call to kvm --version takes ~35ms
> (which i can confirm doing 'time kvm --version')

OK, as expected, but good to have it backed up by numbers.

> so i would say we use the stat approach?

OK for me.

> or are you preferring saving the version into a file?

Seems like a bit more things to do, your solution for stat looks good,
so I would go with that one.

Thanks!