On Tue, 2024-01-16 at 13:33 -0400, Jason Gunthorpe wrote: > On Tue, Nov 28, 2023 at 05:28:36PM +0100, Niklas Schnelle wrote: > > On Mon, 2023-11-27 at 13:51 -0400, Jason Gunthorpe wrote: > > > On Mon, Nov 27, 2023 at 06:43:11PM +0100, Niklas Schnelle wrote: > > > > > > > Also it turns out the writeq() loop we had so far does not produce the > > > > needed 64 byte TLP on s390 either so this actually makes us newly pass > > > > this test. > > > > > > Ooh, that is a significant problem - the userspace code won't be used > > > unless this test passes. So we need this on S390 to fix a bug as well > > > :\ > > > > Yes ;-( > > > > In the meantime I also found out that zpci_write_block(dst, src, 64) is > > not correct for all cases because the PCI store block requires the > > (pseudo-)MMIO write not to cross a 4K boundary and we need src/dst to > > be double word aligned. In rdma-core this is neatly handled by the > > get_max_write_size() but the kernel variant of that > > zpci_get_max_write_size() isn't just a lot harder to read and likely > > less efficient but also too strict thus breaking the 64 byte write up > > needlessly. > > > > In total we have 5 conditions for the PCI block stores: > > > > 1. The dst+len must not cross a 4K boundary in the (pseudo-)MMIO space > > 2. The length must not exceed the maximum write size > > 3. The length must be a multiple of 8 > > 4. The src needs to be double word aligned > > 5. The dst needs to be double word aligned > > > > So I think a good solution would be to improve zpci_memcpy_toio() with > > an enhanced zpci_get_max_write_size() based on the code in rdma-core > > extended to also handle the alignment and length restrictions which in > > rdma-core are already assumed (see comment there). Then we can use > > zpci_memcpy_toio(dst, src, 64) for memcpy_toio_64() and rely on the > > compiler to optimize out the unnecessary checks (2, 3 and possibly 4, > > 5). > > > > So yeah this is getting a bit more complicated than originally > > thought. Let me cook up a patch. > > Did you come up with something? > > Jason Hi Jason, Sorry I haven't replied. Yes, I have a fix for zpci_memcpy_toio() titled "s390/pci: fix max size calculation in zpci_memcpy_toio()" that I tested with this series plus the following define added to arch/s390/include/asm/io.h: #define memcpy_toio_64 zpci_memcpy_toio(dst, src, 64) It's already in the s390 tree's feature branch and linux-next. Thanks, Niklas
