Re: [Tracker] [PATCH] Improve performance of log_output()

[Jürg Billeter <j bitron ch>]

Hi Jim,

On Fri, 2011-03-25 at 18:18 -0700, Jim Kukunas wrote:
> While profiling CPU usage, I noticed that everytime tracker writes
> to a log file, it invokes localtime(3) to generate the timestamp. This
> is less than ideal, because localtime(3) is a relatively expensive
> function.

The idea is that tracker is running with low log verbosity during
regular operation, at least on embedded devices. Due to that, I don't
consider log performance very important myself. I also expect the I/O
part of logging to be more expensive than localtime(3). However, maybe
there is a reason why you need to enable verbose logging in a situation
where performance matters, so let's discuss the patch.

> The attached patch changes the behavior in tracker-log.c to invoke
> localtime(3) only once, during the invocation of tracker_log_init, and
> then use gettimeofday to update the time relative to the time returned
> by the initial localtime(3).

If I read the patches correctly, it will print incorrect timestamps if
the UTC offset changes (DST or timezone change) after tracker_log_init.
While this might not happen very often, I consider it important that the
output is correct as debugging could be very confusing with wrong
timestamps. I assume that timezone handling is also the reason for
localtime(3) being slow.

In the case that log performance is important to you, it might make more
sense to optionally support logging with Unix or UTC timestamps. The
former would definitely be faster, the latter presumably as well.

Regards,
JÃrg