On 05/30/2011 05:43 PM, Ingo Molnar wrote:
> I agree that using the cpu to clear memory is not a good idea, it > just causes cache pollution. Yeah, but even cache-neutral clearing (either driven from the CPU from the idle thread or by a DMA engine) is not a particularly good idea: because it uses up a finite resource: memory bandwidth.
I think that on modern machines it's not such an issue, at least compared to cpu time.
Can we create 'idle' DMA transactions - once that never get in the way of real DMA transactions?
Not to my knowledge.
Also, a profile of a typical kernel build shows: 0.69% cc1 [kernel.kallsyms] [k] clear_page_c 0.49% cc1 [kernel.kallsyms] [k] page_fault So while we could improve it, the question is, can we do this without accidentally slowing things down by more than 0.69%? And kernel builds are a pretty clear_page_c() intense workload.
I usually see much higher clear_page_c, but I'm using a pretty old system for most of my testing.
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