is ccache working effectively?

Magnus Ihse Bursie magnus.ihse.bursie at oracle.com
Tue Nov 20 11:49:06 UTC 2018


On 2018-11-09 11:09, Maurizio Cimadamore wrote:
> That does the trick, thanks.
If ccache and PCH is so bad in combination, maybe we should not allow 
it? Like turning off PCH by default of --enacle-ccache is given? Or at 
least *warn* that this combination is no good?

/Magnus
>
> I take a very small hit in the cold cache case, but then I get huge 
> boost once the cache is hot.
>
> cache hit (direct)                  1629
> cache hit (preprocessed)             115
> cache miss                             1
> cache hit rate                     99.94 %
> cleanups performed                     0
> files in cache                      5121
> cache size                         317.6 MB
> max cache size                       5.0 GB
>
> And, in my laptop the clean/build time went down from 11 mins to 3 :-)
>
> Maurizio
>
> On 09/11/2018 00:24, Erik Joelsson wrote:
>> You can try --disable-precompiled-headers and see if that helps. We 
>> have had special considerations for combining these features in the 
>> past, but it's certainly a source of trouble for ccache.
>>
>> /Erik
>>
>>
>> On 2018-11-08 16:20, Maurizio Cimadamore wrote:
>>>
>>> On 08/11/2018 20:31, Erik Joelsson wrote:
>>>> I think we need more details here to figure it out, but it doesn't 
>>>> surprise me that hotspot is the part that's failing. Building 
>>>> hotspot is way more complex than the rest. 
>>>
>>> Digging more into the command lines of the various HS files, they 
>>> include many generated sources and, also this folder:
>>>
>>> build/<CONF>/hotspot/variant-server/libjvm/objs/precompiled
>>>
>>> Now, I don't know exactly how ccache deals with PCH but I notices 
>>> that every time that the files in this folder are regenerated by the 
>>> build (I can easily do that by rerunning the same command line that 
>>> is stored inside the , a ccache miss follows.
>>>
>>> Maurizio
>>>
>>



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