[yocto] Server specs for a continuous integration system

[Christian Gagneraud]

On 04/09/13 07:22, Chris Tapp wrote:
>
> On 3 Sep 2013, at 00:29, Christian Gagneraud wrote:
>
>> On 03/09/13 10:16, Chris Tapp wrote:
>>> 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.
>>
>> Hi Chris,
>>
>>> 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 ;-)
>>
>> Thanks for the info, i will have a look at RAID-1, as you can see, I know absolutely nothing about RAID! ;)
>
> Did you see my correction to this? I meant to say RAID 0. Sorry for the confusion.

No problem, at least it forces me to look at RAID-5, RAID-1 and now 
RAID-0, thanks! ;)

>
>> Does SSD really help with disk throughput? Then what's the point of using ramdisk for TMPDIR/WORKDIR? If you "fully" work in RAM, the disk bottleneck shouldn't be such a problem anymore (basically, on disk, you should only have your yocto source tree and your download directory?).
>
> Running from RAM would be fastest - it really comes down to how much you have and how much you want to keep.
>
>>
>>>
>>>>>> - 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 have the same configuration here (4 cores, 8 threads), although, i didn't try to tweak bitbake, but i've noticed the same phenomenon as you: even with "aggressive" parallelism settings, the machine wasn't optimally loaded over 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 ;-)
>>
>> The quantity of RAM boils down to the budget, after a (very) quick search, i have estimated the cost of 64GB of RAM to be 1500 to 2000 US$.
>
> That sounds high - I generally get 16GB DDR 1600 for less that 150 US$ - it was quite a bit lower a year back!
>
>>
>> Thanks.
>> Chris
>>
>>
>>>
>>>>
>>>>>   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
>>>
>>>
>>>
>>
>
> Chris Tapp
>
> opensource at keylevel.com
> www.keylevel.com
>
>
>