[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v2] Xen: Spread boot time page scrubbing across all available CPU's
>>> On 30.09.13 at 17:42, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote: > On 30/09/13 16:35, Jan Beulich wrote: >>>>> On 30.09.13 at 15:56, Malcolm Crossley <malcolm.crossley@xxxxxxxxxx> >>>>> wrote: >>> The difference between 1 core per node bandwidth and 3 core's per node >>> bandwidth is: >>> >>> AMD: 30000MB/s (1-core) vs 48000MB/s (3-core) >>> Intel: 12000MB/s (1-core) vs 38000MB/s (3-core) >>> >>> So I think it's worth the extra complexity to have multiple core's per >>> node scrubbing memory. >> The numbers are convincing. Which means that the only request >> I'd have is to avoid more than one hyperthread on a core to get >> picked for doing the scrubbing. > > Why? Being independent operations, scrubbing like this will still be > sped up by hyperthreading. > > As scrubbing RAM is simply a race to get it done as quickly as possible, > unless it can be demonstrated that using all cores is actively > detrimental to the overall time taken, we really should use all cores > where possible. As long as the actual scrubbing routine is written well enough (to saturate the store bandwidth of a single core), having two threads compete with one another for the store ports can only be negatively affecting performance. _If_ multiple hyper- threads would really turn out to be beneficial, that would thus rather be an indication to improve clear_page() (or whatever is being used for the actual scrubbing). Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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