On Mon, Apr 30, 2018 at 11:05:48AM -0400, John Ferlan wrote:
On 04/23/2018 08:28 AM, Daniel P. Berrangé wrote:
Rather than specialcasing handling of the '*' character, use fnmatch() to get normal shell wildcard syntax, as described in 'man glob(7)'.
To get an indication of the performance impact of using globs instead of plain string matches, a test program was written. The list of all 260 log categories was extracted from the source. Then a typical log filters setup was picked by creating an array of the strings "qemu", "security", "util", "cgroup", "event", "object". Every filter string was matched against every log category. Timing information showed that using strstr() this took 8 microseconds, while fnmatch() took 114 microseconds.
IOW, fnmatch is 14 times slower than our existing strstr check. These numbers show a worst case scenario that wil never be hit, because it
s/wil/will
is rare that every log category would have data output. The log category matches are cached, so each category is only checked once no matter how many log statements are emitted. IOW despite being slower, this will be lost in the noise and have no consequence on real world logging performance.
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com> --- src/util/virlog.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
Reviewed-by: John Ferlan <jferlan@redhat.com>
John
BTW: So whether this is available "everywhere" is a bit of an unknown to me - as in strstr would seemingly work on every arch, but fnmatch has this linux-ism wildcard thing going on which leaves a slight bit of doubt in my mind...
NB, we rely on gnulib to provide us fnmatch on all platforms Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|