And Here I Thought buildworld/makeworld Was IO Bound

[Tim Daneliuk]

On 02/09/2014 11:45 PM, army.of.root wrote:
> Am 10/02/14 04:43, schrieb Tim Daneliuk:
>> For some years now, I have been doing nightly builds of -STABLE
>> on an old Pentium D machine with 2G of memory.  Buildworld + 2
>> different kernels was taking in the neighborhood of 3 1/2 hours or so
>> to run.
>>
>> I then upgraded the Mobo/CPU to a Haswell Quadcore I5-4570 and, sure
>> enough, the build time for all the above came down to 30-35 mins or so.
>>
>> "So", says I, "I'll bet a faster drive would help considering all the
>> scribbling to the disk the compilers and makes do".  So, I upgdared to
>> a Kingston SSD Now 300, 120G hard drive and he time to do the above
>> went down to .... wait, it's still about 30-35 mins ????
>>
>> So, I've tried fiddling with different values for -j on the make
>> command line to little avail.  Well, -j8 and -j16 show no real
>> difference here.
>>
>> So is the bounding function here actually CPU not IO?  Am I missing
>> something?
>>
>> Thanks,
>>
>> P.S.  Trying now with no -j arg on make invocation.
>
> Hi,
>
> the new machine has a lot more memory, I assume.

Yes, 8G as opposed to 2G. I suppose I could bump it out
to 16G and see if this makes any material difference with
even more cache space.

> The build probably will not even hit the disk due to caching.


Well ... it has to hit the disk sooner or later.  But, if the
frequency of physical writes is low because of aggregated
IO from the cache, I guess that would tend to make the whole
business more CPU bound than IO bound.  I just found this surprising.

>
> Also remember, the build process spawns probably millions of processes and that alone takes some time.
>
> And 30min sounds pretty great to me :D

Yeah, I wonder what other people are seeing for a full buildworld/kernel and/or what
the master machines at FreeBSD.org do in this regards.

Would anyone else care to share with the class?

>
> Best regards


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Tim Daneliuk     tundra at tundraware.com
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