 | | | Dual-core & Parallel Compile Issues | Dual-core & Parallel Compile Issues 2005-12-07 - By Brian Long
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On Tue, 2005-12-06 at 19:02 -0700, Stephen J. Smoogen wrote:
> On 12/6/05, Brian Long <brilong@(protected)> wrote:
> > Hello folks,
> >
> > I'm grasping at straws here hoping someone else has run into issues
> > running dual-core Opterons (Sun V40z specifically). When we run a large
> > parallel compile with various j values (i.e. -j8, -j16, -j24, -j32,
> > -j40), we are able to compile the end product in much less time on a
> > quad single-core V40z (quad Opteron 852 / 2.6GHz) than on a quad
> > dual-core V40z (quad Opteron 875 / 2.2GHz). For example, with -j20, 7.4
> > mins vs. 9.6 mins without ClearCase and 13.7 mins. vs. 18.6 mins with
> > ClearCase). We have tried on the U5 and U6 kernel with zero improvement
> > seen between the two.
> >
> > When compiling with large -j values on the dual-core system, the CPUs
> > stay 80% idle the majority of the time (as measured by sar on 10-sec
> > interval). On the single-core system, the CPU is much more utilized
> > throughout the build. I can provide graphs if anyone is interested. We
> > have not yet tried to duplicate the issue on RHEL 4 U2, but plan to try
> > in the next few days.
> >
> > I would appreciate any pointers on how we might further investigate what
> > is causing the bottleneck. Are there known issues with the RHEL 3
> > kernel scheduler or anything else I should be aware of? Thanks.
> >
>
> Well I would check to see where the scaling problem occurs to see if
> it is a problem with dual core or going above 4 processors (or both)?
> The tests I would try would be the following:
>
> 1 Single Core CPU vs 1 Double Core CPU (UP versus SMP test)
> 2 Single Core CPU vs 1 Double Core CPU (SMP versus SMP test)
> 4 Single Core CPU vs 2 Double Core CPU (Bigger scale issue)
> 4 Single Core CPU vs 4 Double Core CPU (greater than 4 cpus test)
Stephen,
Thanks for replying. I failed to mention that we also see issues on the
Sun V20z platform. For example, a dual single-core V20z (dual Opteron
252 / 2.6GHz) vs. a dual dual-core V20z (dual Opteron 275 / 2.2 GHz)
running a make -j24, the single-core box finishes in 7.6 mins. and the
dual-core box takes 11.1 mins without ClearCase. With ClearCase in the
mix, the single-core takes 14.9 mins. and the dual-core takes 18.1
mins. :-(
I believe this eliminates the idea that it's a "greater-than-4 (See http://han-4.ora-code.com)-CPU"
issue.
/Brian/
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Brian Long | | |
IT Data Center Systems | .|||. .|||.
Cisco Linux Developer | ..:|||||||:...:|||||||:..
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