Quoting Kenneth Graunke (2017-08-31 21:17:58) > We can drop the meaningless "64" suffix - libdrm_intel originally had > an "offset" field that was an "unsigned long" which was the wrong size, > and we couldn't remove/alter that field without breaking ABI, so we had > to add a uint64_t "offset64" field. > > "presumed_offset" is a bit more descriptive than "offset".
Another aspect is that is used as a hint by the kernel for where to place the object, so offset_hint, request_offset both apply. But once you start mixing in EXEC_OBJECT_PINNED, it is no more presumed. I would suggest that presumed_offset is perhaps a little misleading considering all the possible uses, and would suggest gtt_offset instead. /* * Offset of the buffer inside the Graphics Translation Table. * * This is effectively our GPU address for the buffer and we use it * as our base for all state pointers into the buffer. However, since the * kernel may be forced to move it around during the course of the * buffer's lifetime, we can only know where the buffer was on the last * execbuf. We presume, and are usually right, that the buffer will not * move and so we use that last offset for the next batch and by doing * so we can avoid having the kernel perform a relocation fixup pass as * our pointers inside the batch will be using the correct base offset. * * Since we do use it as a base address for the next batch of pointers, * the kernel treats our offset as a request, and if possible will * arrange the buffer to placed at that address (trying to balance * the cost of buffer migration versus the cost of performing * relocations). Furthermore, we can force the kernel to place the buffer, or * report a failure if we specified a conflicting offset, at our chosen * offset by specifying EXEC_OBJECT_PINNED. * * Note the GTT may be either per context, or shared globally across the * system. On a shared system, our buffers have to contend for address * space with both aperture mappings and framebuffers and so are more * likely to be moved. On a full ppGTT system, each batch exists in its * own GTT, and so each buffer may have their own offset within each * context. */ _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/mesa-dev
