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From "Lu, Yingqi" <>
Subject RE: Listeners buckets and duplication w/ and w/o SO_REUSEPORT on trunk
Date Wed, 29 Oct 2014 17:20:58 GMT
Hi All,

I just want to check if there is any feedback/comments on this? 

For details, please refer to Yann Ylavic's notes and my responses below.


-----Original Message-----
From: Lu, Yingqi []
Sent: Friday, October 10, 2014 4:56 PM
Subject: RE: Listeners buckets and duplication w/ and w/o SO_REUSEPORT on trunk

Dear All,

Attached patch is generated based on current trunk. It covers for prefork/worker/event/eventopt
MPM. It supposes to address following issues regarding to SO_RESUEPORT support vs. current
trunk version:

1. Same as current trunk version implementation, when active_CPU_num <= 8 or when so_reuseport
is not supported by the kernel, ap_num_buckets is set to 1. In any case, there is 1 dedicated
listener per bucket.

2. Remove global variables (mpm_listen, enable_default_listeners and num_buckets). mpm_listen
is changed to MPM local. enabled_default_listener is completely removed. num_buckets is changed
to MPM local (ap_num_buckets). I rename have_so_reuseport to ap_have_so_reuseport. The reason
for keeping that global is because this variable is being used by ap_log_common(). Based on
the feedback here, I think it may not be a good idea to change the function interface. 

3. Change ap_duplicated_listener to have more parameters. This function is being called from
MPM local (prefork.c/worker.c/event.c/eventopt.c). In this function, prefork_listener (or
worker_listener/even_listener/etc) array will be initialized and be set value. ap_num_buckets
is also calculated inside this function. In addition, this version solves the issue with "one_process"
case (current trunk version has issue with one_process enabled).

4. Change ap_close_listener() back to previous (2.4.X version). 

5. Change dummy_connection back to previous (2.4.X version).

6. Add ap_close_duplicated_listeners(). This is called from mpms when stopping httpd.

7. Add ap_close_child_listener(). When listener_thread (child process in prefork) exit, only
the dedicated listener needs to be closed (the rest are already being closed in child_main
when the child process starts).

8. Remove duplication of listener when ap_num_buckets = 1 or without SO_REUSEPORT support
(ap_num_buckets = 1). With so_reuseport, only duplicated (ap_num_buckets - 1) listeners (1
less duplication less current trunk implementation).

9. Inside each mpm, move child_bucket, child_pod and child_mutex (worker/prefork only) to
a struct. Also, add member bucket to the same struct. 

Please review and let me know your feedback. 


-----Original Message-----
From: Yann Ylavic []
Sent: Tuesday, October 07, 2014 5:26 PM
To: httpd
Subject: Re: Listeners buckets and duplication w/ and w/o SO_REUSEPORT on trunk

On Wed, Oct 8, 2014 at 2:03 AM, Yann Ylavic <> wrote:
> On Wed, Oct 8, 2014 at 1:50 AM, Lu, Yingqi <> wrote:
>> 3. Yes, I did use some extern variables. I can change the name of them to better
coordinate with the variable naming conversion. We should do something with ap_prefixed? Is
there anything else I should consider when I rename the variable?
> Maybe defining new functions with more arguments (to be used by the 
> existing ones with NULL or default values) is a better alternative.

For example, ap_duplicate_listeners could be modified to provide mpm_listen and even do the
computation of num_buckets and provide it (this is not an API change since it is trunk only
for now).

ap_close_listeners() could be then restored as before (work on ap_listeners only) and ap_close_duplicated_listeners(mpm_listen)
be introduced and used in the MPMs instead.

Hence ap_listen_rec *mpm_listeners could be MPM local, which would then call ap_duplicate_listeners(...,
&mpm_listeners, &num_buckets) and ap_close_duplicated_listeners(mpm_listeners)

That's just a quick thought...

> Please be aware that existing AP_DECLAREd functions API must not change though.
> Regards,
> Yann.
>> Thanks,
>> Yingqi
>> -----Original Message-----
>> From: Yann Ylavic []
>> Sent: Tuesday, October 07, 2014 4:19 PM
>> To: httpd
>> Subject: Listeners buckets and duplication w/ and w/o SO_REUSEPORT on 
>> trunk
>> Hi,
>> some notes about the current implementation of this (trunk only).
>> First, whether or not SO_REUSEPORT is available, we do duplicate the listeners.
>> This, I think, is not the intention of Yingqi Lu's original proposal, and probably
my fault since I asked for the patch to be splitted in two for a better understanding (finally
the SO_REUSEPORT patch only has been commited).
>> The fact is that without SO_REUSEPORT, this serves nothing, and we'd better use one
listener per bucket (as originally proposed), or a single bucket with no duplication (as before)
if the performance gains do not worth it.
>> WDYT?
>> Also, there is no opt-in/out for this functionalities, nor a way to configure number
of buckets ratio wrt number of CPUs (cores).
>> For example, SO_REUSEPORT also exists on *BSD, but I doubt it would work as expected
since IFAICT this not the same thing as in Linux (DragonFly's implementation seems to be closed
to Linux' one though).
>> Yet, the dynamic setsockopt() check will also succeed on BSD, and the functionality
be enabled.
>> So opt in (my preference) or out?
>> Finally, some global variables (not even ap_ prefixed) are used to communicate between
listen.c and the MPM. This helps not breaking the API, but this is trunk...
>> I guess we can fix it, this is just a (self or anyone's) reminder :)
>> Regards,
>> Yann.
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