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Re: [Xen-devel] alloc_heap_pages is low efficient with more CPUs

>>> On 15.10.12 at 17:45, Keir Fraser <keir@xxxxxxx> wrote:
> On 15/10/2012 14:27, "tupeng212" <tupeng212@xxxxxxxxx> wrote:
>> Please try the attached patch.
>> : Great!  you have done a good job, needless time decreases badly to 1s.
>> If anybody has no proposal, I suggest you to commit this patch.
> I have applied it to xen-unstable. It probably makes sense to put it in 4.1
> and 4.2 as well (cc'ed Jan, and attaching the backport for 4.1 again).

Will do, but do you have an explanation how this simple, memory
only operation (64 CPUs isn't that many) has this dramatic an
effect on performance. Are we bouncing cache lines this badly? If
so, which one(s)? I don't see what would be written frequently
from multiple CPUs here - tlbflush_filter() itself only reads global
variables, but never writes them.


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