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List:       libvir-list
Subject:    Re: [libvirt] [PATCH v2 3/4] log: support logging using shell wildcard syntax
From:       John Ferlan <jferlan () redhat ! com>
Date:       2018-04-30 15:05:48
Message-ID: 76a0d9dd-4ed4-733d-494a-4808ca8844b1 () redhat ! com
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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...

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