RFR: JDK-8144312: Remove limitations on the default number of jobs in the build

[David Holmes]

On 11/12/2015 11:16 PM, Magnus Ihse Bursie wrote:
> On 2015-12-03 03:11, Roger Riggs wrote:
>> Hi,
>>
>> It would be useful to figure out the number of cpus available when in
>> a container.
>> Some comments have added to:
>> 8140793 <https://bugs.openjdk.java.net/browse/JDK-8140793>
>> getAvailableProcessors may incorrectly report the number of cpus in
>> Docker container
>>
>> But so far we haven't dug deep enough.   Suggestions are welcome?
> http://serverfault.com/questions/691659/count-number-of-allowed-cpus-in-a-docker-container
> suggests running nproc. I'm not sure if that can be counted on to be
> present, but we could certainly check for it.

I'd like to know how nproc does it so we can try to apply the same logic 
in the VM for Runtime.availableProcessors. Can someone actually confirm 
that it returns the number of processors available to the container?

David

> /Magnus
>
>>
>> Roger
>>
>>
>> On 12/2/15 6:59 PM, Martin Buchholz wrote:
>>> Not to say you shouldn't do this, but I worry that increasingly
>>> computing
>>> is being done in "containers" where e.g. the number of cpus is doubling
>>> every year but only a small number are available to actually be used
>>> by a
>>> given process.  if availableProcessors reports 1 million, what should we
>>> do?  (no need to answer...)
>>>
>>> On Tue, Dec 1, 2015 at 1:55 AM, Erik Joelsson <erik.joelsson at oracle.com>
>>> wrote:
>>>
>>>> Hello,
>>>>
>>>> The current heuristic for figuring out what to default set the -j
>>>> flag to
>>>> make needs some tweaking.
>>>>
>>>> In JDK 9, it looks at the amount of memory and the number of cpus in
>>>> the
>>>> system. It divides memory by 1024 to get a safe number of jobs that
>>>> will
>>>> fit into memory. The lower of that number and the number of cpus is
>>>> then
>>>> picked. The number is then scaled down to about 90% of the number of
>>>> cpus
>>>> to leave some resources for other activities. It is also capped at 16.
>>>>
>>>> Since we now have the build using "nice" to make sure the build isn't
>>>> bogging down the system, I see no reason to do the 90% scaling anymore.
>>>> Also, the performance issues that forced us to cap at 16 have long been
>>>> fixed, and even if we don't scale well beyond 16, we do still scale.
>>>> So I
>>>> propose we remove that arbitrary limitation too.
>>>>
>>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8144312
>>>> Webrev: http://cr.openjdk.java.net/~erikj/8144312/webrev.01/
>>>>
>>>> /Erik
>>>>
>>
>