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

[Philippe Mathieu-Daudé]

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.

If we want to use pool of runners to restrict transfer between
runners from the same physical pool, then it because a maintenance
headache.