Re: [PATCH 1/4] x86_64: (SPARSE_VIRTUAL doubles sparsemem speed)

Andi Kleen
2007-04-07T22:19:08Z

On Sunday 08 April 2007 00:06:13 Christoph Lameter wrote:

> Results:
>
> x86_64 boot with virtual memmap
>
> Format: #events totaltime (min/avg/max)
>
> kfree_virt_to_page 598430 5.6ms(3ns/9ns/322ns)
>
> x86_64 boot regular sparsemem
>
> kfree_virt_to_page 596360 10.5ms(4ns/18ns/28.7us)
>
>
> On average sparsemem virtual takes half the time than of sparsemem.

Nice. But on what workloads?

Anyways it looks promising. I hope we can just
replace old style sparsemem support with this for x86-64.

> Time is measured using the cycle counter (TSC on IA32, ITC on IA64) which has
> a very low latency.

Sorry that triggered my usual RDTSC rant...

Not on NetBurst (hundred of cycles) And on the others (C2,K8) it is a bit dangerous
to measure short code blocks because RDTSC is not guaranteed ordered with the surrounding
instructions.

-Andi