From: Zheng Li Date: Thu, 25 Sep 2014 17:35:02 +0000 (+0100) Subject: oxenstored: reduce syslog call overhead X-Git-Tag: archive/raspbian/4.8.0-1+rpi1~1^2~4204 X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=025a232326ed6fae55a7853262b2f09473cf7983;p=xen.git oxenstored: reduce syslog call overhead We noticed that, if configured to use syslog as the logging backend, every single line of access logging (via the syslog C binding) will call stat on /etc/localtime for 3 times. The rational behind this is probably to detect any timezone changes over time. This is a considerable cost we'd like to avoid, given the intensiveness of our access logging --- we log almost every xenstore status change (for good reason). Also a running Xen host is rarely a mobile environment, so the little benefit can hardly justify the cost. Setting up the TZ environment varialbe can avoid stat calls. Signed-off-by: Zheng Li Reviewed-by: David Scott --- diff --git a/tools/ocaml/xenstored/logging.ml b/tools/ocaml/xenstored/logging.ml index 3d4a3292fd..665b922419 100644 --- a/tools/ocaml/xenstored/logging.ml +++ b/tools/ocaml/xenstored/logging.ml @@ -130,8 +130,17 @@ let string_of_date () = tm.Unix.tm_hour tm.Unix.tm_min tm.Unix.tm_sec (int_of_float (1000.0 *. msec)) +(* We can defer to syslog for log management *) let make_syslog_logger facility = - (* We defer to syslog for log management *) + (* When TZ is unset in the environment, each syslog call will stat the + /etc/localtime file at least three times during the process. We'd like to + avoid this cost given that we are not a mobile environment and we log + almost every xenstore entry update/watch. *) + let () = + let tz_is_set = + try String.length (Unix.getenv "TZ") > 0 + with Not_found -> false in + if not tz_is_set then Unix.putenv "TZ" "/etc/localtime" in let nothing () = () in let write ?level s = let level = match level with