On Thu, Jul 08, 2021 at 02:59:28PM -0600, Jeffrey Hugo wrote: > On Wed, Jul 7, 2021 at 8:41 AM Jeffrey Hugo <jeffrey.l.hugo@xxxxxxxxx> wrote: > > > > On Wed, Jul 7, 2021 at 3:30 AM Arnd Bergmann <arnd@xxxxxxxx> wrote: > > > > > > On Tue, Jul 6, 2021 at 6:20 PM Will Deacon <will@xxxxxxxxxx> wrote: > > > > > > > > I think the million dollar question is whether the 128-byte cache-lines > > > > live in a cache above the PoC or not. If it's just a system level cache > > > > through which all DMA is "coherent", then it doesn't matter. > > > > > > On Wed, Jul 7, 2021 at 10:24 AM Yassine Oudjana > > > <y.oudjana@xxxxxxxxxxxxxx> wrote: > > > > > > > > On Wednesday, July 7th, 2021 at 12:33 AM, Arnd Bergmann <arnd@xxxxxxxx> wrote: > > > > > On Tue, Jul 6, 2021 at 7:15 PM Yassine Oudjana y.oudjana@xxxxxxxxxxxxxx wrote: > > > > > > > > > > > > $ numactl -C 0 line -M 1M > > > > > > 128 > > > > > > $ numactl -C 3 line -M 1M > > > > > > 128 > > > > > > > > > > Can you rerun the the 'line' test with '-M 128K' to see if that confirms the 64 > > > > > byte L1 line size that the 'cache' test reported? > > > > > > > > $ numactl -C 0 line -M 128K > > > > 64 > > > > $ numactl -C 3 line -M 128K > > > > 64 > > > > > > Ok, so this seems to confirm that the L1 uses 64 byte lines, while the L2 (or > > > possibly L3) uses 128 byte lines. > > > > > > On Wed, Jul 7, 2021 at 12:27 AM Bjorn Andersson > > > <bjorn.andersson@xxxxxxxxxx> wrote: > > > > > > > > I can confirm that MSM8996, and a few derivatives, has 128 byte cache lines. > > > > > > Ok, thanks. Assuming this is an outer cache and the L1 indeed has a smaller line > > > size, can you also confirm that this 128 byte lines are north of the point of > > > coherency? > > > > Finding this old documentation has been painful :) > > > > L0 I 64 byte cacheline > > L1 I 64 > > L1 D 64 > > L2 unified 128 (shared between the CPUs of a duplex) > > > > I believe L2 is within the POC, but I'm trying to dig up the old > > documentation to confirm. > > Was able to track down a friendly hardware designer. The POC lies > between L2 and L3. Hope this helps. Damn, yes, it's bad news but thanks for chasing it up. I'll revert the patch at -rc1 and add a comment about MSM8996. Will
