Re: [PATCH 00/27] Latest numa/core release, v16

[Mel Gorman]

On Mon, Nov 19, 2012 at 11:36:04PM +0100, Ingo Molnar wrote:
> 
> * Mel Gorman <mgorman@xxxxxxx> wrote:
> 
> > Ok.
> > 
> > In response to one of your later questions, I found that I had 
> > in fact disabled THP without properly reporting it. [...]
> 
> Hugepages is a must for most forms of NUMA/HPC.

Requiring huge pages to avoid a regression is a mistake.

> This alone 
> questions the relevance of most of your prior numa/core testing 
> results. I now have to strongly dispute your other conclusions 
> as well.
> 

I'll freely admit that disabling THP for specjbb was a mistake and I should
have caught why at the start. However, the autonumabench figures reported for
the last release had THP enabled as had the kernel build benchmark figures.

> Just a look at 'perf top' output should have told you the story.
> 

I knew THP were not in use and said so in earlier reports. Take this for
example -- https://lkml.org/lkml/2012/11/16/207 . For specjbb, note that
the THP fault alloc figures are close to 0 and due to that I said "THP is
not really a factor for this workload". What I failed to do was identify
why THP was not in use.

> Yet time and time again you readily reported bad 'schednuma' 
> results for a slow 4K memory model that neither we nor other 
> NUMA testers I talked to actually used, without stopping to look 
> why that was so...
> 

Again, I apologise for the THP mistake. The fact remains that the other
implementations did not suffer a performance slowdown due to the same
mistake.

> [ I suspect that if such terabytes-of-data workloads are forced 
>   through such a slow 4K pages model then there's a bug or 
>   mis-tuning in our code that explains the level of additional 
>   slowdown you saw - we'll fix that.
> 
>   But you should know that behavior under the slow 4K model 
>   tells very little about the true scheduling and placement 
>   quality of the patches... ]
> 
> Please report proper THP-enabled numbers before continuing.
> 

Will do. Are THP-disabled benchmark results to be ignored?

-- 
Mel Gorman
SUSE Labs
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/