On Tue, May 15, 2012 at 11:15:29PM +0200, Alfredo Finelli wrote:
> Mark Hindley:
> > Thanks.
> >
> > From a purely selfish apt-cacher point of view we don't call select()
> > directly, it is only through IO::Select. Although I am reluctant to
> > deflect the blame, I think this maybe a perl-base bug.
> >
> > Could you try this script and play with the timeout value in
> > $select->can_read(). Obviously it should print an elapsed time for each
> > loop of the order of the can_read timeout. I get something of the
> > correct order right down to 1us (perl 5.10.1). What do you get?
>
> Here my results.
OK, I accept that this is not working properly on faster systems (than I
have). Actually the impact on response time and throughput is not as
great as I had previously thought either. This is my proposed solution
-- I would be grateful if you could test that it fixes it for you. I
have implemented a new configuration option curl_throttle with a default
of 1 (equivalent to 1ms). You could persuade me the default should be
10ms :)
Mark
commit d5b2f01b423954e823306ee587ee95b0dd867ef5
Author: Mark Hindley <m...@hindley.org.uk>
Date: Wed May 16 14:09:29 2012 +0100
Implement curl_throttle to control libcurl CPU usage. Value is number of
milliseconds IO::Select->can_read() will wait for a new connection before
timing
out and continuing to fetch.
diff --git a/apt-cacher b/apt-cacher
index 775b008..c90d9f0 100755
--- a/apt-cacher
+++ b/apt-cacher
@@ -1482,7 +1482,7 @@ sub connect_curlm {
# timeout here which also prevents the parent while
# loop from running too fast and hogging the CPU
# uselessly.
- if ($active_handles && $select->can_read(0.00001)) {
+ if ($active_handles &&
$select->can_read($cfg->{curl_throttle}/1000)) {
$cfg->{debug} && debug_message('Pending
connection');
next LIBCURL_REQUEST;
}
diff --git a/debian/apt-cacher.8 b/debian/apt-cacher.8
index 26c140c..fa0ed44 100644
--- a/debian/apt-cacher.8
+++ b/debian/apt-cacher.8
@@ -415,6 +415,12 @@ closing the connection.
The maximum time in seconds the libcurl backend will wait, unused, before
exiting.
.TP
+.B curl_throttle [1]
+Controls how fast the libcurl process runs. Increasing this setting will reduce
+the CPU load of the libcurl process, possibly at the expense of slower response
+times and a lower throughput. On most systems this option should be left
+unchanged.
+.TP
.B request_empty_lines [5]
The number of empty lines tolerated before an incoming connection is closed.
.TP
diff --git a/lib/apt-cacher.pl b/lib/apt-cacher.pl
index 1a460ea..f1ec427 100755
--- a/lib/apt-cacher.pl
+++ b/lib/apt-cacher.pl
@@ -38,6 +38,7 @@ sub read_config {
}
$count},
curl_idle_timeout => 120,
+ curl_throttle => 1,
daemon_port => 3142,
debug => 0,
denied_hosts => '',
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