[yocto] Server specs for a continuous integration system

[Chris Tapp]

On 2 Sep 2013, at 22:45, Christian Gagneraud wrote:

> 
> On 03/09/13 00:35, Burton, Ross wrote:
> 
> Hi Ross,
> 
>> On 2 September 2013 06:05, Christian Gagneraud <chgans at gna.org> wrote:
>>> So right now, I'm thinking about:
>>> - CPU: Xeon E5, maybe 2 x E5-2670/90, for a total of 16 cores (32 threads)
>>> - Hard drives: 500GB, 1 TB or 2 TB (ideally with RAID if it can speed up the
>>> builds)
> 
> RAID-5 seems to be what i am after.

Isn't RAID-5 going to be slower, especially if it's software? RAID 1 is probably better as you'll potentially double the write speed to disk. I use a couple of Vertex SSDs in RAID 1 giving a theoretical write speed near to 1GBs. Write endurance is possibly a concern, but I've not had any issues using them on a local build machine. I would probably look at some higher end models if I was going to run a lot of builds. A lot less noise than hard drives ;-)

>>> - RAM: i don't really know, maybe 8 or 16 GB or more?
>> 
>> At least 16GB of RAM for the vast amount of disk cache that will give
>> you.  32GB or more will mean you can easily put the TMPDIR or WORKDIR
>> into a tmpfs (there's been discussion about this a few weeks ago).
> 
> Yes, I remember that one now, well spotted!
> 
>> I've 16GB of RAM and a 8GB tmpfs with rm_work was sufficient for
>> WORKDIR which gave a 10% speedup (and massive reduction on disk wear).
> 
> I'm a bit surprise to see only a 10% speedup.

I looked at this a while back on a quad core + hyper-threading system (so 8 cores). Depending on what you're building, there are significant periods of the build where even 8 cores aren't maxed out as there's not enough on the ready list to feed to them - basically there are times when you're not CPU, memory or I/O bound. I've estimated that being able to max out the CPUs would cut 20-25% of the build time, but the build-time dependencies mean this isn't easy/possible. At one point I inverted the priority scheme used by the bitbake scheduler and it (very surprisingly) made no difference to the overall build time!

I ran builds with 16 threads and 16 parallel makes and the peak memory usage I see is something like 8GB during intensive compile/link phases, so 16GB for RAM and tmpfs sounds like a reasonable minimum. The tmpfs would reduce SSD wear quite a bit ;-)

> 
>>  Others have machines with 64GB RAM and use it for all of TMPDIR, at
>> which point you'll be almost entirely CPU-bound.
> 
> OK, so 16GB sounds like a minimum, 32GB or 64GB being even better, at that size, this is not that cheap...
> 
> Thanks,
> 
> Chris
> 
>> 
>> Ross
>> 
> 
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Chris Tapp

opensource at keylevel.com
www.keylevel.com