How to read and write to Global Data Share in AMD GCN?


I'm trying to use GDS in AMD GPU, but I can not make it work. My GPU is AMD RX580.

I used this OpenCL kernel:

__kernel __attribute__((reqd_work_group_size(64, 1, 1)))

void localVarExample(__global int *res)
  int i = get_global_id(0);
  __local int x;
  if (i == 0) {
    x = 0;
  if (i == 0) {
    *res = x;

Built it and disassembled with (CLRX ). After that I added gds flag into DS instructions and modified M0 register.

So I got this ASM kernel:

/* Disassembling 'barrier-Ellesmere.bin' */
.gpu Iceland
.arch_minor 0
.arch_stepping 4
.driver_version 203603
.compile_options "-fno-bin-source -fno-bin-llvmir -fno-bin-amdil -fbin-exe -D__AMD__=1 -D__Ellesmere__=1 -D__Ellesmere=1 -D__IMAGE_SUPPORT__=1 -DFP_FAST_FMA=1 -cl-denorms-are-zero -m64 -Dcl_khr_fp64=1 -Dcl_amd_fp64=1 -Dcl_khr_global_int32_base_atomics=1 -Dcl_khr_global_int32_extended_atomics=1 -Dcl_khr_local_int32_base_atomics=1 -Dcl_khr_local_int32_extended_atomics=1 -Dcl_khr_int64_base_atomics=1 -Dcl_khr_int64_extended_atomics=1 -Dcl_khr_3d_image_writes=1 -Dcl_khr_byte_addressable_store=1 -Dcl_khr_fp16=1 -Dcl_khr_gl_sharing=1 -Dcl_khr_gl_depth_images=1 -Dcl_amd_device_attribute_query=1 -Dcl_amd_vec3=1 -Dcl_amd_printf=1 -Dcl_amd_media_ops=1 -Dcl_amd_media_ops2=1 -Dcl_amd_popcnt=1 -Dcl_khr_d3d10_sharing=1 -Dcl_khr_d3d11_sharing=1 -Dcl_khr_dx9_media_sharing=1 -Dcl_khr_image2d_from_buffer=1 -Dcl_khr_spir=1 -Dcl_khr_subgroups=1 -Dcl_khr_gl_event=1 -Dcl_khr_depth_images=1 -Dcl_khr_mipmap_image=1 -Dcl_khr_mipmap_image_writes=1 -Dcl_amd_liquid_flash=1 -Dcl_amd_planar_yuv=1"
.acl_version "AMD-COMP-LIB-v0.8 (0.0.SC_BUILD_NUMBER)"
.kernel localVarExample
        .dims x
        .cws 64, 1, 1
        .sgprsnum 13
        .vgprsnum 3
        .localsize 4
        .floatmode 0xc0
        .gdssize 0x1000
        .pgmrsrc1 0x00ac0040
        .pgmrsrc2 0x0000008c
        .priority 0
        .arg _.global_offset_0, "size_t", long
        .arg _.global_offset_1, "size_t", long
        .arg _.global_offset_2, "size_t", long
        .arg _.printf_buffer, "size_t", void*, global, , rdonly
        .arg _.vqueue_pointer, "size_t", long
        .arg _.aqlwrap_pointer, "size_t", long
        .arg res, "int*", int*, global, 
        s_mov_b32       s7, 0x1000
        s_mov_b32       m0, s7                          # Setup M0 register with GDS size == 0x1000.
        s_lshl_b32      s0, s6, 6                       # #s0 = s6 * 64 (== group_id * local_size).
        s_load_dwordx2  s[2:3], s[4:5], 0x0             # Load global_offset_0 into s[2:3].
        s_waitcnt       lgkmcnt(0)
        s_add_u32       s0, s0, s2                      # s0 += s2. Now s0 = group_id * local_size + global_offset_0.
        v_add_u32       v0, vcc, s0, v0                 # v0 += s0. Now v0 = get_global_id(0).
        v_cmp_lg_i32    s[0:1], v0, 0                   # | 
        s_mov_b64       s[2:3], exec                    # |  if (get_global_id(0) == 0)
        s_andn2_b64     exec, s[2:3], s[0:1]            # |
        v_mov_b32       v0, 0x0
        s_cbranch_execz .L64_0
        ds_write_b32    v0, v0 gds                      # write 0 to the first uint32 in GDS (only the first thread do this).
        s_mov_b64       exec, s[2:3]
        v_mov_b32       v0, 0
        v_mov_b32       v1, 1
        s_waitcnt       lgkmcnt(0)
        ds_add_u32      v0, v1 gds                      # Atomic increment the first uint32 in GDS  (v0 is address, v1 is value).
        s_waitcnt       lgkmcnt(0)                      # wait for ds_add_u32
        s_andn2_b64     exec, s[2:3], s[0:1]            # |  if (get_global_id(0) == 0)  reuse SGPR from previous if.
        v_mov_b32       v0, 0
        s_cbranch_execz .L140_0                         # Finish all threads exept by the first one .
        s_load_dwordx2  s[0:1], s[4:5], 0x30            # Load res argument into s[0:1]. s[0:1] == &res[0] now.
        ds_read_b32     v0, v0 gds                      # Read from the first uint32 in GDS into v0.
        s_waitcnt       lgkmcnt(0)                      # Wait for ds_add_u32.
        v_mov_b32       v1, s0                            
        v_mov_b32       v2, s1
        flat_store_dword v[1:2], v0                     # Save v0 into res[0]

I fill res with 0 in host program. The expected result is res[0] == 64. And OpenCL kernel with LDS works this way. But in GDS version res[0] == 0.

asked on Stack Overflow Jul 8, 2019 by Michael Lukin

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