Re: [Xen-devel] [PATCHv2 5/5] evtchn: pad struct evtchn to 64 bytes

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 15.06.15 at 17:48, <david.vrabel@xxxxxxxxxx> wrote:
> The number of struct evtchn in a page must be a power of two.  Under
> some workloads performance is improved slightly by padding struct
> evtchn to 64 bytes (a cache line), thus putting the per-channel locks
> into their own cache line.
> 
> This does not decrease the number of struct evtchn's per-page.
> 
> Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
> ---
> I'm not sure we actually want to do this.  I think it would be better
> to pack the struct evtchn and use vmap to turn the pages into a linear
> array for quicker lookup.

But then you'd end up with two locks on one cache line again. I.e.
I can see the possible benefit of making the tree a linear table, but
I don't see how that eliminates the desire for the change here.

Jan


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