Re: [PATCH v3 4/6] gitlab-ci: Add ccache in $PATH and display statistics

["Philippe Mathieu-Daudé" <f4bug@amsat.org>]

On 5/21/21 4:21 PM, Philippe Mathieu-Daudé wrote:
> On 5/21/21 2:52 PM, Daniel P. Berrangé wrote:
>> On Fri, May 21, 2021 at 02:27:26PM +0200, Philippe Mathieu-Daudé wrote:
>>> On 5/21/21 1:53 PM, Daniel P. Berrangé wrote:
>>>> On Fri, May 21, 2021 at 01:02:51PM +0200, Thomas Huth wrote:
>>>>> On 21/05/2021 12.50, Daniel P. Berrangé wrote:
>>>>>> On Fri, May 21, 2021 at 12:48:21PM +0200, Thomas Huth wrote:
>>>>>>> On 20/05/2021 13.27, Philippe Mathieu-Daudé wrote:
>>>>>>>> +Stefan/Daniel
>>>>>>>>
>>>>>>>> On 5/20/21 10:02 AM, Thomas Huth wrote:
>>>>>>>>> On 19/05/2021 20.45, Philippe Mathieu-Daudé wrote:
>>>>>>>>>> If a runner has ccache installed, use it and display statistics
>>>>>>>>>> at the end of the build.
>>>>>>>>>>
>>>>>>>>>> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
>>>>>>>>>> ---
>>>>>>>>>>     .gitlab-ci.d/buildtest-template.yml | 5 +++++
>>>>>>>>>>     1 file changed, 5 insertions(+)
>>>>>>>>>>
>>>>>>>>>> diff --git a/.gitlab-ci.d/buildtest-template.yml
>>>>>>>>>> b/.gitlab-ci.d/buildtest-template.yml
>>>>>>>>>> index f284d7a0eec..a625c697d3b 100644
>>>>>>>>>> --- a/.gitlab-ci.d/buildtest-template.yml
>>>>>>>>>> +++ b/.gitlab-ci.d/buildtest-template.yml
>>>>>>>>>> @@ -6,13 +6,18 @@
>>>>>>>>>>           then
>>>>>>>>>>             JOBS=$(sysctl -n hw.ncpu)
>>>>>>>>>>             MAKE=gmake
>>>>>>>>>> +        PATH=/usr/local/libexec/ccache:$PATH
>>>>>>>>>>             ;
>>>>>>>>>>           else
>>>>>>>>>>             JOBS=$(expr $(nproc) + 1)
>>>>>>>>>>             MAKE=make
>>>>>>>>>> +        PATH=/usr/lib/ccache:/usr/lib64/ccache:$PATH
>>>>>>>>>
>>>>>>>>> That does not make sense for the shared runners yet. We first need
>>>>>>>>> something to enable the caching there - see my series "Use ccache in the
>>>>>>>>> gitlab-CI" from April (which is currently stalled unfortunately).
>>>>>>>>
>>>>>>>> TL;DR: I don't think we should restrict our templates to shared runners.
>>>>>>>
>>>>>>> I'm certainly not voting for restricting ourselves to only use shared
>>>>>>> runners here - but my concern is that this actually *slows* down the shared
>>>>>>> runners even more! (sorry, I should have elaborated on that in my previous
>>>>>>> mail already)
>>>>>>>
>>>>>>> When I was experimenting with ccache in the shared runners, I saw that the
>>>>>>> jobs are running even slower with ccache enabled as long as the cache is not
>>>>>>> populated yet. You only get a speedup afterwards. So if you add this now
>>>>>>> without also adding the possibility to store the cache persistently, the
>>>>>>> shared runners will try to populate the cache each time just to throw away
>>>>>>> the results afterwards again. Thus all the shared runners only get slower
>>>>>>> without any real benefit here.
>>>>>>>
>>>>>>> Thus we either need to get ccache working properly for the shared runners
>>>>>>> first, or you have to think of a different way of enabling ccache for the
>>>>>>> non-shared runners, so that it does not affect the shared runners
>>>>>>> negatively.
>>>>>>
>>>>>> Is there anything functional holding up your previous full cccache support
>>>>>> series from last month ? Or is it just lack of reviews ?
>>>>>
>>>>> It's basically the problems mentioned in the cover letter and Stefan's
>>>>> comment here:
>>>>>
>>>>>  https://lists.gnu.org/archive/html/qemu-devel/2021-04/msg02219.html
>>>>
>>>> I'm not sure I understand why Stefan thinks gitlab's caching doesn't
>>>> benefit ccache. We add ccache for libvirt GitLab CI, and AFAIR it
>>>> sped up our builds significantly.
>>>
>>> I think Stefan is referring to a comment I made, when using both
>>> shared runners and dedicated runners (what I'm currently testing)
>>> various jobs are stuck transferring artifacts/cache {FROM, TO}
>>> {shared, dedicated} runners at the same time, which is sub-optimal
>>> because it saturate the dedicated runner network link.

FYI In case we need to sort this out later, the 'resource_group' might
help us with this:
https://docs.gitlab.com/ee/ci/yaml/#resource_group

>> I think we're over thinking things a bit too much and worrying about
>> scenarios that we're not actually hitting that frequently today, and
>> delaying the benefit for everyone.
>>
>> Our common case is that most contributors are simply using shared
>> runners exclusively, as is the main qemu repo staging branch. AFAIK
>> these should benefit from a simple ccache enablement today.
>>
>> Since there are questions about other setups though, we can just
>> provide an easy way to turn it off. eg:
>>
>>   if test -z "$QEMU_CI_SKIP_CCACHE"
>>   then
>>      PATH=/usr/local/libexec/ccache:$PATH
>>   fi
>>
>> anyone who wishes to disable it, can just set that variable in their
>> git repo fork. If there are specific jobs we want to disable cccache
>> for, those jobs can set that too.
> 
> OK, understood. I'll see with Willian how to have ccache working.
> 
> Thanks for the feedback,
> 
> Phil.
>