On 21 September 2015 at 09:44, David Woods <dwoods@xxxxxxxxxx> wrote: > > Steve, Hi Dave, > > Thanks for your review and comments. I take your points about the 16k > granule - it's helpful to know that support is in the works. However, I'm > not sure I agree with your reading of section 4.4.2. It's clear that for 16k > granules, the number of contiguous pages is different for the PTE and PMD > levels. But I don't see anywhere it says that for 4K and 64K that the > contig bit is not supported at the PMD level - just that the number of > contiguous pages is the same at each level. Many apologies, I appear to have led you down the garden path there. Having double checked at ARM, the valid contiguous page sizes are indeed: 4K granule: 16 x ptes = 64K 16 x pmds = 32M 16 x puds = 16G 16K granule: 128 x ptes = 2M 32 x pmds = 1G 64K granule: 32 x ptes = 2M 32 x pmds = 16G > > I tried using the tarmac trace module of the ARM simulator to support this > idea by turning on MMU tracing. Using 4k granule, I created 64k and 32m > pages and touched each location in the page. In both cases, the trace > recorded just one TLB fill (rather than the 16 you'd expect if the > contiguous bit were being ignored) and it indicated the expected page size. > > 1817498494 clk cpu2 TLB FILL cpu2.S1TLB 64K 0x2000000000_NS vmid=0, nG > asid=303:0x08fa360000_NS Normal InnerShareable Inner=WriteBackWriteAllocate > Outer=WriteBackWriteAllocate xn=0 pxn=1 ContiguousHint=1 > > 1263366314 clk cpu2 TLB FILL cpu2.UTLB 32M 0x2000000000_NS vmid=0, nG > asid=300:0x08f6000000_NS Normal InnerShareable Inner=WriteBackWriteAllocate > Outer=WriteBackWriteAllocate xn=0 pxn=1 ContiguousHint=1 > > I'll try this with a 64k granule next. I'm not sure what will happen with > 16G pages since we are using an A53 model which I don't think supports such > large pages. The Cortex-A53 supported TLB sizes can be found in the TRM: http://infocenter.arm.com/help/topic/com.arm.doc.ddi0500f/Chddiifa.html My understanding is that the core is allowed to ignore the contiguous bit if it doesn't support the particular TLB entry size, or substitute in a slightly smaller TLB entry than hinted possible. Anyway, do give it a go :-). Cheers, -- Steve -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>