Re: build erlang with kqueue support

Thank you for your time
and insightful explanations!

Bogdan

On Tue, Nov 16, 2021 at 11:48 AM Lukas Larsson <[email protected]> wrote:

>
>
> On Tue, Nov 16, 2021 at 10:30 AM Bogdan Andu <[email protected]> wrote:
>
>> Great,
>>
>> I have the following:
>>
>> 2> erlang:system_info(check_io).
>> [[{name,erts_poll},
>>   {primary,poll},
>>  * {kernel_poll,false},*
>>   {memory_size,12920},
>>   {total_poll_set_size,2},
>>   {lazy_updates,true},
>>   {pending_updates,0},
>>   {batch_updates,false},
>>   {concurrent_updates,false},
>>   {fallback,true},
>>   {max_fds,512},
>>   {active_fds,0},
>>   {poll_threads,0}],
>>  [{name,erts_poll},
>>   {primary,kqueue},
>>   *{kernel_poll,kqueue},*
>>   {memory_size,56},
>>   {total_poll_set_size,1},
>>   {lazy_updates,false},
>>   {pending_updates,0},
>>
>>
>>   {batch_updates,false},
>>
>>
>>   {concurrent_updates,true},
>>
>>
>>   {fallback,false},
>>
>>
>>   {max_fds,512},
>>
>>
>>   {active_fds,0},
>>
>>
>>   {poll_threads,0}],
>>
>>
>>  [{name,erts_poll},
>>   {primary,kqueue},
>>   *{kernel_poll,kqueue},*
>>   {memory_size,28728},
>>   {total_poll_set_size,1},
>>   {lazy_updates,false},
>>   {pending_updates,0},
>>   {batch_updates,false},
>>   {concurrent_updates,true},
>>   {fallback,false},
>>   {max_fds,512},
>>   {active_fds,0},
>>   {poll_threads,1}]]
>> 3>
>>
>> What means *{kernel_poll,false}* ?
>> That poll is not used and kqueue it is used?
>>
>> Why are three poll entries and why one kernel-poll kqueue entry has
>> memory_size 56 and the next has memory_size 28728? Which one is used by
>> the emulator?
>>
>
> Different OSs need different polling strategies, for OpenBSD (and others,
> I can't recall which) there are by default 3 pollsets used.
>
> 1) The first pollset is what is called the fallback pollset and it is used
> for any FD that cannot be polled by kqueue. I think that the stdin/stdout
> fds end up here and possibly some others.
> 2) The main pollset used by the poll-thread for most I/O polling. This is
> why this pollset is larger.
> 3) An optimized pollset where the read side of any fd that uses the
> `{active,true}` pattern is placed. Mainly this is used for distribution
> sockets, but works for any other fd as well that follows this pattern.
>
>
>> And how can I customize the parameters like max_fds, total_poll_set_size,
>> memory_size?
>>
>
> Max fds is taken from `ulimit -n` of the current user. The other values
> are just statistics about the current usage.
>
>
>> And how does these parameters impact the performance of busy erlang node
>> like say,
>> very high traffic tcp/ip/ssl server?
>>
>
> They don't. These values are meant for debugging the system, not
> optimizing it. If you are interested in optimizing you may want to read
> this blog post: https://www.erlang.org/blog/io-polling/.
>
> However, from the I/O polling point of view things are quite optimal in
> the default setting. So I doubt that you can gain much by tweaking the
> different options available.
>
>
>>
>> Thank you,
>>
>>
>> On Tue, Nov 16, 2021 at 11:07 AM Lukas Larsson <[email protected]> wrote:
>>
>>> On Tue, Nov 16, 2021 at 9:59 AM Bogdan Andu <[email protected]> wrote:
>>>
>>>> Hi Lukas,
>>>>
>>>> I didn't; find any documentation related to that.
>>>>
>>>
>>> A pr improving the documentation would be much appreciated!
>>>
>>>
>>>>
>>>> Anyway,
>>>>
>>>> $ erl
>>>> Erlang/OTP 24 [erts-12.1.4] [source] [64-bit] [smp:4:4] [ds:4:4:10]
>>>> [async-threads:1]
>>>>
>>>> Eshell V12.1.4  (abort with ^G)
>>>> 1> erlang:system_info(kernel_poll).
>>>> true
>>>> 2>
>>>>
>>>> I guess I have kernel poll support for my erlang servers.
>>>>
>>>> How can one tell if it is 'kqueue' or 'poll' type of kernel poll?
>>>>
>>>> Because OpenBSD has also poll which is not great
>>>>
>>>> Is there any erlang system information function that shows
>>>> exactly that?
>>>>
>>>
>>> If you run `erlang:system_info(check_io)` you will get information about
>>> the I/O checking sub-system which should include information about which
>>> mechanism is used.
>>>
>>>
>>>>
>>>> Thank you
>>>>
>>>>
>>>>
>>>> On Tue, Nov 16, 2021 at 10:53 AM Lukas Larsson <[email protected]>
>>>> wrote:
>>>> >
>>>> > Hello!
>>>> >
>>>> > The banner about kernel-poll was removed from the erlang start some
>>>> releases ago. So to check if you have kernel poll support you need to call
>>>> `erlang:system_info(kernel_poll)`. If it returns `true` then you have
>>>> kernel-poll support.
>>>> >
>>>> > Lukas
>>>> >
>>>> > On Tue, Nov 16, 2021 at 9:47 AM Bogdan Andu <[email protected]> wrote:
>>>> >>
>>>> >> Hello,
>>>> >>
>>>> >> I have an OpenBSD 6.8 amd64 machine and
>>>> >> I would like to compile Erlang 24 with kqueue support
>>>> >> such that I want erl to show me this:
>>>> >>
>>>> >> $erl
>>>> >> ........................ [kernel-poll]
>>>> >>
>>>> >> I understand that this is a compile time option
>>>> >> and not anymore a runtime selectable option tru + K true
>>>> >> switch
>>>> >>
>>>> >> I tried the following configure options with no success:
>>>> >> ./configure --prefix=/usr/local/erlang24.1.4
>>>> >> --with-ssl=/usr/local/openssl/1.1.1l --enable-dynamic-ssl-lib
>>>> >> --with-ssl-rpath=/usr/local/openssl/1.1.1l/lib --without-javac
>>>> >> --enable-threads --enable-kernel-poll --disable-hipe
>>>> >>
>>>> >> With openbsd patches (+./otp_build update_configure)
>>>> >> and without patches the result is the same:
>>>> >> no kernel-poll flag present - meaning that kernel polling with kqueue
>>>> >> is not available to that erlang emulator.
>>>> >>
>>>> >> Please advice me how to build erlang 24 with kqueue support.
>>>> >>
>>>> >> I have an Openbsd 5.4 with erlang 19 that does has kernell-poll flag
>>>> >>
>>>> >> $ erl +Ktrue
>>>> >> Erlang/OTP 19 [erts-8.1] [source] [64-bit] [smp:2:2]
>>>> >> [async-threads:10] [kernel-poll:true]
>>>> >>
>>>> >> Eshell V8.1  (abort with ^G)
>>>> >>
>>>> >>
>>>> >> p.s.
>>>> >> building erlang 24 against openssl 1.1.1 for tlsv3 support wasn't
>>>> >> a pleasant experience. The configuration script links against
>>>> >> system libressl  openssl library, instead of --with-ssl option given
>>>> >> to ./configure.
>>>> >> So I had to alter manually crypto ./configure and Makefile files .
>>>>
>>>