On Tue, 2019-12-10 at 16:20 +0100, Jan Beulich wrote: > > ol2e = l2e_from_intpte( > l2e_get_intpte(ol2e) + (PAGE_SIZE << > PAGETABLE_ORDER)); > > Of course, as mentioned before, I'm not overly happy to see type > safety lost in case like this one, where it's not needed like e.g. > further up to convert from L3 to L2 entry. >
Okay, so I did a comparison between the efficiency of the assembly under a release build. The old "type-safe" way requires 16 instructions to prepare the first l2e, and each iteration of the inner loop of populating l2t requires 7 instructions. The new type-unsafe way requires 6 to prepare the first l2e, and each iteration of populating l2t takes 5 instructions. So the difference of populating l2t is 3600 vs. 2566 instructions, which is not very small. I have not tested the packed bit field way you suggested, but I think it could even be higher than 3600 due to masking, shifting and also overflow handling. Hongyan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
