Re: [PATCH i-g-t 2/2] tests/intel/xe_prefetch_fault: add L2 prefetch fault subtests

Hi Varun,
On 2026-08-18 at 10:57:16 +0530, Varun Gupta wrote:
> Add L2 prefetch fault testing. When L1 cache policy is
> set to uncached (UC), the prefetch bypasses LSC and is sourced from L2
> instead.
> 
> Add a new shader gpgpu_shader__l2_prefetch_fault() that uses message
> descriptor 0x49C00 (L1UC_L2C_L3UC, cache control value 4) instead of
> the existing 0x99C00 (L1C_L2C_L3C, cache control value 9). Only bits
> [19:16] of the descriptor differ.

When you add a new shader you also need to add it to compiled
source in tests/intel/xe_prefetch_fault.c.gen.iga64_codes.c

Now linking on armhf fails with:

[1314/1800] Linking target tests/xe_prefetch_fault
FAILED: tests/xe_prefetch_fault 
/usr/bin/arm-linux-gnueabihf-gcc  -o tests/xe_prefetch_fault tests/xe_prefetch_fault.p/intel_xe_prefetch_fault.c.o -Wl,--as-needed -Wl,--no-undefined -Wl,--start-group lib/libigt.so.0 /usr/lib/arm-linux-gnueabihf/libcairo.so /usr/lib/arm-linux-gnueabihf/libglib-2.0.so /usr/lib/arm-linux-gnueabihf/libdrm.so /usr/lib/arm-linux-gnueabihf/libdw.so /usr/lib/arm-linux-gnueabihf/libelf.so /usr/lib/arm-linux-gnueabihf/libkmod.so /usr/lib/arm-linux-gnueabihf/libpci.so /usr/lib/arm-linux-gnueabihf/libudev.so -lm /usr/lib/arm-linux-gnueabihf/libpciaccess.so /usr/lib/arm-linux-gnueabihf/libpixman-1.so -pthread -lrt -lz /usr/lib/arm-linux-gnueabihf/libdrm_nouveau.so /usr/lib/arm-linux-gnueabihf/libdrm_amdgpu.so /usr/lib/arm-linux-gnueabihf/libunwind.so /usr/lib/arm-linux-gnueabihf/libgsl.so /usr/lib/arm-linux-gnueabihf/libgslcblas.so /usr/lib/arm-linux-gnueabihf/libasound.so -Wl,--end-group '-Wl,-rpath,$ORIGIN/../lib' -Wl,-rpath-link,/opt/builds/build/lib
/usr/lib/gcc-cross/arm-linux-gnueabihf/10/../../../../arm-linux-gnueabihf/bin/ld: tests/xe_prefetch_fault.p/intel_xe_prefetch_fault.c.o: in function `gpgpu_shader__l2_prefetch_fault':
/opt/builds/build/../tests/intel/xe_prefetch_fault.c:97: undefined reference to `iga64_code_xe_l2_prefetch_fault_prefetch'
collect2: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.

+cc Andrzej Hajda



Regards,
Kamil

> 
> Add two new subtests:
>   - l2-prefetch-fault: validates L2 prefetch fault with unmapped address
>     followed by hit-under-miss with mapped page
>   - l2-prefetch-fault-svm: same as above but in SVM mode with HMM-backed
>     CPU page table resolution
> 
> Signed-off-by: Varun Gupta <[email protected]>
> ---
>  tests/intel/xe_prefetch_fault.c | 97 +++++++++++++++++++++++++++++++++
>  1 file changed, 97 insertions(+)
> 
> diff --git a/tests/intel/xe_prefetch_fault.c b/tests/intel/xe_prefetch_fault.c
> index e86cd68d9..4843f56fd 100644
> --- a/tests/intel/xe_prefetch_fault.c
> +++ b/tests/intel/xe_prefetch_fault.c
> @@ -81,6 +81,56 @@ L0:
>  	)", lower_32_bits(addr), upper_32_bits(addr));
>  }
>  
> +/**
> + * gpgpu_shader__l2_prefetch_fault:
> + * @shdr: shader to be modified
> + * @addr: ppgtt virtual address to raise L2 prefetch fault
> + *
> + * This shader can only be used when in efficient 64bit mode.
> + * For a given arbitrary ppgtt virtual address, it raises an L2 prefetch fault
> + * using load instruction with L1 uncached + L2 cached cache policy.
> + * With L1 uncached, the prefetch bypasses LSC and is sourced from L2.
> + */
> +static void gpgpu_shader__l2_prefetch_fault(struct gpgpu_shader *shdr,
> +					    uint64_t addr)
> +{
> +	igt_assert_f((addr & 0x7) == 0, "address must be aligned to QWord!\n");
> +
> +	emit_iga64_code(shdr, xe_l2_prefetch_fault_prefetch, R"(
> +#define IGA64_FLAGS ""
> +#if GFX_VER >= 4000
> +#elif GFX_VER >= 3500
> +L0:
> +// Set base address with scalar register
> +(W)	mov (1)		s0.0<1>:ud		ARG(0):ud
> +(W)	mov (1)		s0.1<1>:ud		ARG(1):ud
> +
> +// A64 offset
> +(W)	mov (8)		r30.0<1>:uq		0x0:uq
> +
> +// efficient 64bit Read with uncached L1, cached L2 and uncached L3
> +// sendg ugm load - L2 prefetch (L1 bypass)
> +// Message Descriptor
> +//      DP_LOAD_STORE_STATELESS_DESC (HAS:2209865465)
> +//      DP_CACHE_LOAD (HAS:2209865465) value 4 = L1UC_L2C_L3UC
> +//      0x49C00 =>
> +//      [45:44] Offset Scaling: 0 (disable)
> +//      [43:22] Global Offset: 0
> +//      [21] Overfetch: 0 (disable)
> +//      [19:16] Cache: 4 (L1 uncached, L2 cached and L3 uncached)
> +//      [15:14] Address Type and Size: 2 (Flat A64 Base, A64 Index)
> +//      [13:11] Data Size: 3 (D64)
> +//      [10:10] Transpose : 1 (enable)
> +//      [9:7] Vector Size: 0 (Vector length 1)
> +//      [5:0] Opcode: 0 (Load)
> +// Prefetch operations are implemented using a NULL destination register.
> +// L1 uncached forces the prefetch to bypass LSC, making L2 the fault source.
> +(W)	sendg.ugm (1|M0)	null	r30:1	null:0	s0.0	0x49C00	{A@1,$5}
> +
> +#endif
> +	)", lower_32_bits(addr), upper_32_bits(addr));
> +}
> +
>  static struct intel_buf *
>  create_buf(int fd, int width, int height, uint32_t color)
>  {
> @@ -130,6 +180,17 @@ static struct gpgpu_shader *get_prefetch_shader(int fd)
>  	return shader;
>  }
>  
> +static struct gpgpu_shader *get_l2_prefetch_shader(int fd)
> +{
> +	struct gpgpu_shader *shader;
> +
> +	shader = gpgpu_shader_create(fd);
> +	gpgpu_shader__l2_prefetch_fault(shader, xe_canonical_va(fd, PREFETCH_ADDR));
> +	gpgpu_shader__eot(shader);
> +
> +	return shader;
> +}
> +
>  /**
>   * SUBTEST: prefetch-fault
>   * Description: Validate L1 prefetch fault and hit-under-miss behavior with
> @@ -140,6 +201,16 @@ static struct gpgpu_shader *get_prefetch_shader(int fd)
>   * Description: Validate L1 prefetch fault and hit-under-miss behavior in SVM
>   *		mode with L1 cached, L2 cached cache policy (fault source: LSC)
>   * Run type: FULL
> + *
> + * SUBTEST: l2-prefetch-fault
> + * Description: Validate L2 prefetch fault and hit-under-miss behavior with
> + *		L1 uncached, L2 cached cache policy (fault source: L2)
> + * Run type: FULL
> + *
> + * SUBTEST: l2-prefetch-fault-svm
> + * Description: Validate L2 prefetch fault and hit-under-miss behavior in SVM
> + *		mode with L1 uncached, L2 cached cache policy (fault source: L2)
> + * Run type: FULL
>   */
>  static void test_prefetch_fault(int fd, struct drm_xe_engine_class_instance *hwe,
>  				bool svm, get_shader_fn get_shader)
> @@ -296,6 +367,32 @@ int igt_main()
>  		}
>  	}
>  
> +	igt_subtest_with_dynamic("l2-prefetch-fault") {
> +		xe_for_each_engine(fd, hwe) {
> +			if (hwe->engine_class == DRM_XE_ENGINE_CLASS_RENDER ||
> +			    hwe->engine_class == DRM_XE_ENGINE_CLASS_COMPUTE) {
> +				igt_dynamic_f("%s%d", xe_engine_class_string(hwe->engine_class),
> +					      hwe->engine_instance)
> +					test_prefetch_fault(fd, hwe, false,
> +							    get_l2_prefetch_shader);
> +			}
> +		}
> +	}
> +
> +	igt_subtest_with_dynamic("l2-prefetch-fault-svm") {
> +		if (!svm_supported)
> +			igt_skip("SVM not supported on this device, skipping.\n");
> +		xe_for_each_engine(fd, hwe) {
> +			if (hwe->engine_class == DRM_XE_ENGINE_CLASS_RENDER ||
> +			    hwe->engine_class == DRM_XE_ENGINE_CLASS_COMPUTE) {
> +				igt_dynamic_f("%s%d", xe_engine_class_string(hwe->engine_class),
> +					      hwe->engine_instance)
> +					test_prefetch_fault(fd, hwe, true,
> +							    get_l2_prefetch_shader);
> +			}
> +		}
> +	}
> +
>  	igt_fixture() {
>  		drm_close_driver(fd);
>  	}
> -- 
> 2.43.0
>