Turn on UseNUMA by default when prudent

[Jesper Wilhelmsson]

I can sponsor this change if the rest of the GC team is OK with the change. Or does it have to be a formal reviewer?
/Jesper


1 jun 2012 kl. 17:27 skrev Vladimir Kozlov <vladimir.kozlov at oracle.com>:

> Can GC group sponsor this change? I think we also need to do the same for Solaris (the code is similar there).
> 
> Thanks,
> Vladimir
> 
> On 6/1/12 4:43 AM, Jesper Wilhelmsson wrote:
>> This looks OK to me.
>> /Jesper
>> 
>> 
>> On 2012-05-31 17:05, Eric Caspole wrote:
>>> OK, I removed the warning, see
>>> 
>>> http://cr.openjdk.java.net/~ecaspole/numa_default_3/
>>> 
>>> Thanks,
>>> Eric
>>> 
>>> 
>>> On May 30, 2012, at 4:58 PM, Vladimir Kozlov wrote:
>>> 
>>>> We issue a warning only if something is not right which not the case here:
>>>> 
>>>> + warning("Turned on UseNUMA in os::init_2");
>>>> 
>>>> otherwise looks good.
>>>> 
>>>> Vladimir
>>>> 
>>>> Eric Caspole wrote:
>>>>> I put a much simpler, still linux only rev at
>>>>> http://cr.openjdk.java.net/~ecaspole/numa_default_2/
>>>>> Simply doing UseNUMA on by default might work but there are so many
>>>>> os/platforms to consider it's more than I can try to test.
>>>>> Eric
>>>>> On May 30, 2012, at 4:14 PM, Jesper Wilhelmsson wrote:
>>>>>> On 2012-05-30 20:41, Igor Veresov wrote:
>>>>>>> Actually UseNUMA should already do what you want. Even if specified on
>>>>>>> the command line it will switch itself off if there's only one node present.
>>>>>> 
>>>>>> So, will setting UseNUMA to true as default be a platform independent way
>>>>>> of solving this?
>>>>>> /Jesper
>>>>>> 
>>>>>>> 
>>>>>>> igor
>>>>>>> 
>>>>>>> On May 30, 2012, at 12:27 AM, Thomas Schatzl wrote:
>>>>>>> 
>>>>>>>> Hi all,
>>>>>>>> 
>>>>>>>> On Tue, 2012-05-29 at 21:56 +0200, Jesper Wilhelmsson wrote:
>>>>>>>>> Hi Eric,
>>>>>>>>> 
>>>>>>>>> As long as this is based on actual data and not just a hunch, I personally
>>>>>>>>> think it is a good idea. I don't know if we have any policies about
>>>>>>>>> platform
>>>>>>>>> specific optimizations like this though.
>>>>>>>>> 
>>>>>>>>> I have some comments on the code layout and there are a few typos, but
>>>>>>>>> I guess
>>>>>>>>> this is still a draft so I won't pick on that right now.
>>>>>>>>> 
>>>>>>>>> One thing I wonder though is in os_linux_x86.cpp:
>>>>>>>>> 
>>>>>>>>> if (VM_Version::cpu_family() == 0x15 || VM_Version::cpu_family() ==
>>>>>>>>> 0x10) {
>>>>>>>>> 
>>>>>>>>> Is this the only way to identify the proper processor family? It
>>>>>>>>> doesn't seem
>>>>>>>>> very future proof. How often would you have to change this code to keep
>>>>>>>>> it up
>>>>>>>>> to date with new hardware?
>>>>>>>> just a question, if this is implemented, wouldn't it more prudent to
>>>>>>>> actually check whether the VM process runs on a NUMA machine, and
>>>>>>>> actually has its computing (or memory) resources distributed across
>>>>>>>> several nodes instead of a check for some arbitrary processors and
>>>>>>>> processor identifiers?
>>>>>>>> 
>>>>>>>> This would, given that the OS typically provides this information
>>>>>>>> anyway, also immediately support e.g. sparc setups. It also avoids
>>>>>>>> distributing memory when the user explicitly assigned the VM to a single
>>>>>>>> node...
>>>>>>>> 
>>>>>>>>> From memory, on solaris above mentioned detection works approximately as
>>>>>>>> follows:
>>>>>>>> 
>>>>>>>> - detect the total amount of leaf locality groups (=nodes on Solaris)
>>>>>>>> in the system, e.g. via lgrp_nlgrps()
>>>>>>>> - from the root node (retrieved via lgrp_root()), iterate over its
>>>>>>>> children and leaf lgroups via lgrp_children().
>>>>>>>> - for each of the leaf lgroups found, check whether there is an
>>>>>>>> active cpu for this process in it using lgrp_cpus(); if so, increment
>>>>>>>> counter
>>>>>>>> 
>>>>>>>> Maybe there is a better way to do that though.
>>>>>>>> 
>>>>>>>> On Linux, numa_get_run_node_mask() may provide the same information when
>>>>>>>> called during initialization.
>>>>>>>> On Windows, it seems that a combination of GetProcessAffinityMask() and
>>>>>>>> GetNUMAProcessorNode() may be useful.
>>>>>>>> (From a cursory web search for the latter two; not sure about other
>>>>>>>> OSes, but you could simply provide a dummy for those)
>>>>>>>> 
>>>>>>>> I'd guess that some of the needed functionality to implement this is
>>>>>>>> already provided by the current Hotspot code base.
>>>>>>>> 
>>>>>>>> 
>>>>>>>> Ergonomics stuff is typically handled in runtime/arguments.?pp, so it
>>>>>>>> might be a better place as a location for updating globals than putting
>>>>>>>> this detection in some os-specific initialization code.
>>>>>>>> 
>>>>>>>> Eg.
>>>>>>>> 
>>>>>>>> if (FLAG_IS_DEFAULT(UseNUMA)) {
>>>>>>>> UseNUMA := [maybe some other conditions&&]
>>>>>>>> (os::get_num_active_numa_nodes()> 1);
>>>>>>>> }
>>>>>>>> 
>>>>>>>> in e.g. Arguments::set_ergonomics_flags() or similar.
>>>>>>>> 
>>>>>>>> Seems a lot nicer than an explicit check for some processor family.
>>>>>>>> Maybe a little more work though.
>>>>>>>> 
>>>>>>>> Hth,
>>>>>>>> Thomas
>>>>>>>> 
>>>>>>>> 
>>>>>>>> <jesper_wilhelmsson.vcf>
>>>> 
>>> 
>>>