RFR: 8221535: add steal tick related information to hs_error file [linux]

[David Holmes]

Hi Matthias,

On 2/04/2019 9:04 pm, Baesken, Matthias wrote:
> Hi David ,  thanks for the review .
> 
> New webrev :
> 
> http://cr.openjdk.java.net/~mbaesken/webrevs/8221535.4/
> 
> I  added the blank after if  you suggested and  also  adjusted  the comments  in  bool os::Linux::get_tick_information   slightly .
> 
> May I add you as a reviewer ?

Of course! Reviewed.

>>> I kept the  has_steal_ticks   for now; in case someone  can  confirm
>>> 2.6.11+  for jdk13  I would remove it .
>>
>> I can't comment on that.
>>
> 
> It's a pity  that we do not  have such an info .
> 
> However I found  that we include   <sys/inotify.h>   here :
> 
> http://hg.openjdk.java.net/jdk/jdk/file/69204b98dc3d/src/java.base/linux/native/libnio/fs/LinuxWatchService.c#l36
> 
> and this seems to be  2.6.13+ functionality :
> 
> https://en.wikipedia.org/wiki/Inotify
> 
> "August 29, 2005: Linux kernel version 2.6.13 released, containing merged inotify code"
> 
> However  it is not hotspot coding, so  I am not 100% sure that we really   can claim  2.6.13+   for the whole codebase .

As we no longer attempt to separate the VM from the JDK we implicitly 
acquire the minimum platform constraints of each other. So if the JDK 
already assumes 2.6.13+ then hotspot should be able to safely assume it too.

We checked for inotify capability dynamically in JDK 6 because, in part, 
our build platform was Linux 2.4. But since JDK 7 we have assumed 
inotify is available at build time and runtime. So it seems to me that 
we can quite safely assume here that we are indeed on 2.6.13+

Thanks,
David
-----

> 
> Best regards , Matthias
> 
> 
> 
> 
>> -----Original Message-----
>> From: David Holmes <david.holmes at oracle.com>
>> Sent: Montag, 1. April 2019 07:01
>> To: Baesken, Matthias <matthias.baesken at sap.com>; Thomas Stüfe
>> <thomas.stuefe at gmail.com>
>> Cc: hotspot-dev at openjdk.java.net
>> Subject: Re: RFR: 8221535: add steal tick related information to hs_error file
>> [linux]
>>
>> Hi Matthias,
>>
>> On 29/03/2019 11:37 pm, Baesken, Matthias wrote:
>>> Hello, new webrev :
>>>
>>> http://cr.openjdk.java.net/~mbaesken/webrevs/8221535.3/
>>>
>>> changed the function to bool os::Linux::get_tick_information(cpu_ticks*
>>> out, int which_logical_cpu = -1)
>>
>> Okay.
>>
>>> added memset  at beginning of get_tick_information
>>
>> Okay
>>
>>> removed the remaining vm_printf    from
>>> src/hotspot/os/aix/os_perf_aix.cpp      (at first I did not notice it
>>>    was  there as well ).
>>
>> Okay
>>
>>> [ kept the struct  naming CPUPerfTicks    ( I find plenty of such struct
>>> name  styles  in hotspot codebase  ).   ]
>>
>> Agreed - no consistency and you're moving existing code so this is fine
>> IMHO.
>>
>>>>
>>>
>>>> In case  we  are sure that we are always  on  2.6.11+   kernels, then indeed
>> I can remove the  special handling.
>>>
>>>> I was sure  that  we are on 2.6+  but only 95%  sure that we are
>> on  2.6.11+   .
>>>
>>>>
>>>
>>> I kept the  has_steal_ticks   for now; in case someone  can  confirm
>>> 2.6.11+  for jdk13  I would remove it .
>>
>> I can't comment on that.
>>
>> One nit in os_linux.cpp:
>>
>> +   if((fh = fopen("/proc/stat", "r")) == NULL) {
>>
>> Need space after if
>>
>> Otherwise this all seems fine to me.
>>
>> Thanks,
>> David
>>
>