[Xen-changelog] [xen master] oxenstored: reduce syslog call overhead

[patchbot@xxxxxxx]

commit 025a232326ed6fae55a7853262b2f09473cf7983
Author:     Zheng Li <dev@xxxxxxxx>
AuthorDate: Thu Sep 25 18:35:02 2014 +0100
Commit:     Ian Campbell <ian.campbell@xxxxxxxxxx>
CommitDate: Wed Oct 8 14:28:56 2014 +0100

    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 <dev@xxxxxxxx>
    Reviewed-by: David Scott <dave.scott@xxxxxxxxxx>
---
 tools/ocaml/xenstored/logging.ml |   11 ++++++++++-
 1 files changed, 10 insertions(+), 1 deletions(-)

diff --git a/tools/ocaml/xenstored/logging.ml b/tools/ocaml/xenstored/logging.ml
index 3d4a329..665b922 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
--
generated by git-patchbot for /home/xen/git/xen.git#master

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