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[Bug 53239] Httpd has problems delivering data on rate-limited line

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bugzilla at apache

May 16, 2012, 1:34 AM

Post #1 of 13 (191 views)
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[Bug 53239] Httpd has problems delivering data on rate-limited line

https://issues.apache.org/bugzilla/show_bug.cgi?id=53239

--- Comment #1 from Bjørnar Ness <bjornar.ness [at] gmail> ---
Created attachment 28785
--> https://issues.apache.org/bugzilla/attachment.cgi?id=28785&action=edit
strace -tt -d httpd -X

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bugzilla at apache

May 16, 2012, 2:23 AM

Post #2 of 13 (185 views)
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[Bug 53239] Httpd has problems delivering data on rate-limited line [In reply to]

https://issues.apache.org/bugzilla/show_bug.cgi?id=53239

--- Comment #2 from Bjørnar Ness <bjornar.ness [at] gmail> ---
Created attachment 28786
--> https://issues.apache.org/bugzilla/attachment.cgi?id=28786&action=edit
har-log of site loading in httpd 2.5-trunk

Use:

http://pcapperf.appspot.com/

to view har

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bugzilla at apache

May 16, 2012, 2:24 AM

Post #3 of 13 (185 views)
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[Bug 53239] Httpd has problems delivering data on rate-limited line [In reply to]

https://issues.apache.org/bugzilla/show_bug.cgi?id=53239

--- Comment #3 from Bjørnar Ness <bjornar.ness [at] gmail> ---
Created attachment 28787
--> https://issues.apache.org/bugzilla/attachment.cgi?id=28787&action=edit
har-log of site loading in lighttpd

Use:

http://pcapperf.appspot.com/

to view har

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bugzilla at apache

May 16, 2012, 2:35 AM

Post #4 of 13 (185 views)
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[Bug 53239] Httpd has problems delivering data on rate-limited line [In reply to]

https://issues.apache.org/bugzilla/show_bug.cgi?id=53239

Bjørnar Ness <bjornar.ness [at] gmail> changed:

What |Removed |Added
----------------------------------------------------------------------------
CC| |bjornar.ness [at] gmail

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bugzilla at apache

May 16, 2012, 1:19 PM

Post #5 of 13 (176 views)
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[Bug 53239] Httpd has problems delivering data on rate-limited line [In reply to]

https://issues.apache.org/bugzilla/show_bug.cgi?id=53239

--- Comment #4 from Stefan Fritsch <sf [at] sfritsch> ---
I don't think this is httpd's fault. The strace shows that at 08:14:49.102908,
httpd starts to send data. The socket buffer gets full a few times, httpd uses
poll() to wait each time and sends more data. This works as expected until
08:14:49.105963 when httpd has sent about 75k of data. There, the socket buffer
is full again but the poll() returns only 25 seconds later, at 08:15:15.686502.
This means either there was no data going through the network and the buffer
was really not writable for these 25 seconds, or there is a kernel bug.

Of course, it is rather strange that Apache httpd triggers this problem but it
seems lighttpd doesn't. Accordingly, I have no idea what we could do to avoid
the problem. If the kernel tells us we can't write to the socket, there is
nothing we can do about that.

You could try analyzing the network traffic with wireshark and see if there are
lost packets.

NB: There seems to be an unrelated bug somewhere because the mmap() of the read
file is done at unaligned offsets, which fails and makes httpd fall back to
writev(). I don't see this here on my system. This could be due to you using
apr 2.0 which is unreleased and not stable. I would recommend to use the newest
released versions of apr and apr-util instead (1.4.x).

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bugzilla at apache

May 17, 2012, 10:43 AM

Post #6 of 13 (174 views)
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[Bug 53239] Httpd has problems delivering data on rate-limited line [In reply to]

https://issues.apache.org/bugzilla/show_bug.cgi?id=53239

--- Comment #5 from Bjørnar Ness <bjornar.ness [at] gmail> ---
Created attachment 28800
--> https://issues.apache.org/bugzilla/attachment.cgi?id=28800&action=edit
pcap of transfer (not same as above)

Ingress limited to 200kbps with 20Kb burst

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bugzilla at apache

May 17, 2012, 10:45 AM

Post #7 of 13 (174 views)
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[Bug 53239] Httpd has problems delivering data on rate-limited line [In reply to]

https://issues.apache.org/bugzilla/show_bug.cgi?id=53239

--- Comment #6 from Bjørnar Ness <bjornar.ness [at] gmail> ---
Tried with sendfile disabled (ref:
https://issues.apache.org/bugzilla/show_bug.cgi?id=53253)

No change. Pcap is apache running as worker with sendfile off

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bugzilla at apache

May 18, 2012, 7:14 AM

Post #8 of 13 (174 views)
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[Bug 53239] Httpd has problems delivering data on rate-limited line [In reply to]

https://issues.apache.org/bugzilla/show_bug.cgi?id=53239

--- Comment #7 from Joe Orton <jorton [at] redhat> ---
$ grep 'pid 438.*08:14:49' logfile | sed 's/writev(6, .*) = /writev(6, ....)
= /'
...
[pid 438] 08:14:49.102908 writev(6, ....) = 14480
[pid 438] 08:14:49.103150 writev(6, ....) = -1 EAGAIN (Resource temporarily
unavailable)
[pid 438] 08:14:49.103347 writev(6, ....) = 20272
[pid 438] 08:14:49.103578 writev(6, ....) = -1 EAGAIN (Resource temporarily
unavailable)
[pid 438] 08:14:49.103775 poll([{fd=6, events=POLLOUT}], 1, 60000) = 1
([{fd=6, revents=POLLOUT}])
[pid 438] 08:14:49.103837 writev(6, ....) = 14480

That second writev() call failed with EAGAIN - why did httpd immediately retry
it without first doing a poll()? That looks weird and wrong.

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bugzilla at apache

May 21, 2012, 12:31 AM

Post #9 of 13 (171 views)
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[Bug 53239] Httpd has problems delivering data on rate-limited line [In reply to]

https://issues.apache.org/bugzilla/show_bug.cgi?id=53239

--- Comment #8 from Joe Orton <jorton [at] redhat> ---
Can you reproduce this if using prefork rather than event?

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bugzilla at apache

May 21, 2012, 1:17 AM

Post #10 of 13 (171 views)
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[Bug 53239] Httpd has problems delivering data on rate-limited line [In reply to]

https://issues.apache.org/bugzilla/show_bug.cgi?id=53239

--- Comment #9 from Bjørnar Ness <bjornar.ness [at] gmail> ---
I reproduced with worker atleast, should I also try with prefork -X ?

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bugzilla at apache

May 21, 2012, 4:22 AM

Post #11 of 13 (171 views)
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[Bug 53239] Httpd has problems delivering data on rate-limited line [In reply to]

https://issues.apache.org/bugzilla/show_bug.cgi?id=53239

--- Comment #10 from Bjørnar Ness <bjornar.ness [at] gmail> ---
Created attachment 28808
--> https://issues.apache.org/bugzilla/attachment.cgi?id=28808&action=edit
strace -tt -d /opt/apache/bin/httpd -X > logfile 2>&1

Server version: Apache/2.5.0-dev (Unix)
Server built: May 21 2012 12:27:51
Server's Module Magic Number: 20120211:3
Server loaded: APR 2.0.0-dev
Compiled using: APR 2.0.0-dev
Architecture: 64-bit
Server MPM: prefork
threaded: no
forked: yes (variable process count)

Server compiled with....
-D APR_HAS_SENDFILE
-D APR_HAS_MMAP
-D APR_HAVE_IPV6 (IPv4-mapped addresses disabled)
-D APR_USE_SYSVSEM_SERIALIZE
-D APR_USE_PTHREAD_SERIALIZE
-D SINGLE_LISTEN_UNSERIALIZED_ACCEPT
-D APR_HAS_OTHER_CHILD
-D AP_HAVE_RELIABLE_PIPED_LOGS
-D DYNAMIC_MODULE_LIMIT=256
-D HTTPD_ROOT="/opt/apache"
-D SUEXEC_BIN="/opt/apache/bin/suexec"
-D DEFAULT_PIDLOG="logs/httpd.pid"
-D DEFAULT_SCOREBOARD="logs/apache_runtime_status"
-D DEFAULT_ERRORLOG="logs/error_log"
-D AP_TYPES_CONFIG_FILE="conf/mime.types"
-D SERVER_CONFIG_FILE="conf/httpd.conf"

Compiled in modules:
core.c
mod_authn_file.c
mod_authn_dbm.c
mod_authn_core.c
mod_authz_host.c
mod_authz_user.c
mod_authz_core.c
mod_access_compat.c
mod_auth_basic.c
mod_apreq2.c
mod_request.c
http_core.c
mod_mime.c
mod_log_config.c
mod_logio.c
mod_env.c
mod_headers.c
mod_setenvif.c
mod_proxy.c
mod_proxy_fcgi.c
prefork.c
mod_unixd.c
mod_vhost_alias.c
mod_dir.c
mod_rewrite.c

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bugzilla at apache

May 21, 2012, 4:24 AM

Post #12 of 13 (171 views)
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[Bug 53239] Httpd has problems delivering data on rate-limited line [In reply to]

https://issues.apache.org/bugzilla/show_bug.cgi?id=53239

--- Comment #11 from Bjørnar Ness <bjornar.ness [at] gmail> ---
First download is firefox, second wget

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bugzilla at apache

May 22, 2012, 12:25 AM

Post #13 of 13 (167 views)
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[Bug 53239] Httpd has problems delivering data on rate-limited line [In reply to]

https://issues.apache.org/bugzilla/show_bug.cgi?id=53239

--- Comment #12 from Bjørnar Ness <bjornar.ness [at] gmail> ---
Created attachment 28812
--> https://issues.apache.org/bugzilla/attachment.cgi?id=28812&action=edit
strace -tt -d /opt/lighttpd/sbin/lighttpd

lighttpd running in same vm with same ingress bw limit, but delivering data as
should be expected. ingress limit 200kbps/20KB burst

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