Hi Jason, > > + /* Overwrite the control register with the new buffer size (in 4B words) */ > > + snet_write_ctrl(regs, buf_words); > > + /* Use a memory barrier, this must be written before the opcode register. */ > > + wmb(); > > > At least you need to use smp_wmb() but if you want to serialize MMIO > writes you can simply use spinlocks after the removal of mmiowb > work[1]. > I'm not sure how a spinlock can help in this case. The entire control mechanism is protected by the spinlock snet->ctrl_lock, so multiple CPUs won't use it simultaneously. > Note that Documentation/memory-barriers.txt said: > > 1. All readX() and writeX() accesses to the same peripheral are ordered > with respect to each other. This ensures that MMIO register accesses > by the same CPU thread to a particular device will arrive in program > order. > So it will arrive to the pci subsystem in program order, but the pci subsystem may reorder, right? I can just issue a read after the writes, something like: write_control read_control write op read op What do you think? > > + /* Clear the control register - clear the error code if previous control operation failed */ > > + snet_write_ctrl(regs, 0); > > + > > + /* Write opcode and VQ idx */ > > + val = opcode | (vq_idx << 16); > > + snet_write_op(regs, val); > > I guess we need to serialize two writes here as well. Same here. Thanks _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
