On Mon, Oct 26, 2020 at 09:23:31AM +1100, Gavin Shan wrote: > On 10/25/20 8:52 PM, Marc Zyngier wrote: > > On Sun, 25 Oct 2020 01:27:37 +0100, > > Gavin Shan <gshan@xxxxxxxxxx> wrote: > > > > > > The 52-bits physical address is disabled until CONFIG_ARM64_PA_BITS_52 > > > is chosen. This uses option for that check, to avoid the unconditional > > > check on PAGE_SHIFT in the hot path and thus save some CPU cycles. > > > > PAGE_SHIFT is known at compile time, and this code is dropped by the > > compiler if the selected page size is not 64K. This patch really only > > makes the code slightly less readable and the "CPU cycles" argument > > doesn't hold at all. > > > > So what are you trying to solve exactly? > > > > There are two points covered by the patch: (1) The 52-bits physical address > is visible only when CONFIG_ARM64_PA_BITS_52 is enabled in arch/arm64 code. > The code looks consistent with this option used here. (2) I had the assumption > that gcc doesn't optimize the code and PAGE_SHIFT is always checked in order > to get higher 4 physical address bits, but you said gcc should optimize the > code accordingly. However, it would be still nice to make the code explicit. I don't know: adding #ifdef CONFIG_ lines just reduces the coverage we get from CI, so unless the code is actually causing a problem then I'd be inclined to leave it as-is. Will _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
