[Patch v7 00/24] Support SIMD/eGPRs/SSP registers sampling for perf

Dapeng Mi
2026-03-24T00:45:52Z

Changes since V6:
- Fix potential overwritten issue in hybrid PMU structure (patch 01/24)
- Restrict PEBS events work on GP counters if no PEBS baseline suggested
(patch 02/24)
- Use per-cpu x86_intr_regs for perf_event_nmi_handler() instead of
temporary variable (patch 06/24)
- Add helper update_fpu_state_and_flag() to ensure TIF_NEED_FPU_LOAD is
set after save_fpregs_to_fpstate() call (patch 09/24)
- Optimize and simplify x86_pmu_sample_xregs(), etc. (patch 11/24)
- Add macro word_for_each_set_bit() to simplify u64 set-bit iteration
(patch 13/24)
- Add sanity check for PEBS fragment size (patch 24/24)

Changes since V5:
- Introduce 3 commits to fix newly found PEBS issues (Patch 01~03/19)
- Address Peter comments, including,
* Fully support user-regs sampling of the SIMD/eGPRs/SSP registers
* Adjust newly added fields in perf_event_attr to avoid holes
* Fix the endian issue introduced by for_each_set_bit() in
event/core.c
* Remove some unnecessary macros from UAPI header perf_regs.h
* Enhance b2b NMI detection for all PEBS handlers to ensure identical
behaviors of all PEBS handlers
- Split perf-tools patches which would be posted in a separate patchset
later

Changes since V4:
- Rewrite some functions comments and commit messages (Dave)
- Add arch-PEBS based SIMD/eGPRs/SSP sampling support (Patch 15/19)
- Fix "suspecious NMI" warnning observed on PTL/NVL P-core and DMR by
activating back-to-back NMI detection mechanism (Patch 16/19)
- Fix some minor issues on perf-tool patches (Patch 18/19)

Changes since V3:
- Drop the SIMD registers if an NMI hits kernel mode for REGS_USER.
- Only dump the available regs, rather than zero and dump the
unavailable regs. It's possible that the dumped registers are a subset
of the requested registers.
- Some minor updates to address Dapeng's comments in V3.

Changes since V2:
- Use the FPU format for the x86_pmu.ext_regs_mask as well
- Add a check before invoking xsaves_nmi()
- Add perf_simd_reg_check() to retrieve the number of available
registers. If the kernel fails to get the requested registers, e.g.,
XSAVES fails, nothing dumps to the userspace (the V2 dumps all 0s).
- Add POC perf tool patches

Changes since V1:
- Apply the new interfaces to configure and dump the SIMD registers
- Utilize the existing FPU functions, e.g., xstate_calculate_size,
get_xsave_addr().

Starting from Intel Ice Lake, XMM registers can be collected in a PEBS
record. Future Architecture PEBS will include additional registers such
as YMM, ZMM, OPMASK, SSP and APX eGPRs, contingent on hardware support.

This patch set introduces a software solution to mitigate the hardware
requirement by utilizing the XSAVES command to retrieve the requested
registers in the overflow handler. This feature is no longer limited to
PEBS events or specific platforms. While the hardware solution remains
preferable due to its lower overhead and higher accuracy, this software
approach provides a viable alternative.

The solution is theoretically compatible with all x86 platforms but is
currently enabled on newer platforms, including Sapphire Rapids and
later P-core server platforms, Sierra Forest and later E-core server
platforms and recent Client platforms, like Arrow Lake, Panther Lake and
Nova Lake.

Newly supported registers include YMM, ZMM, OPMASK, SSP, and APX eGPRs.
Due to space constraints in sample_regs_user/intr, new fields have been
introduced in the perf_event_attr structure to accommodate these
registers.

After a long discussion in V1,
https://lore.kernel.org/lkml/3f1c9a9e-cb63-47ff-a5e9-06555fa6cc9a@linux.intel.com/
The below new fields are introduced.

@@ -547,6 +549,25 @@ struct perf_event_attr {

__u64 config3; /* extension of config2 */
__u64 config4; /* extension of config3 */
+
+ /*
+ * Defines set of SIMD registers to dump on samples.
+ * The sample_simd_regs_enabled !=0 implies the
+ * set of SIMD registers is used to config all SIMD registers.
+ * If !sample_simd_regs_enabled, sample_regs_XXX may be used to
+ * config some SIMD registers on X86.
+ */
+ union {
+ __u16 sample_simd_regs_enabled;
+ __u16 sample_simd_pred_reg_qwords;
+ };
+ __u16 sample_simd_vec_reg_qwords;
+ __u32 __reserved_4;
+
+ __u32 sample_simd_pred_reg_intr;
+ __u32 sample_simd_pred_reg_user;
+ __u64 sample_simd_vec_reg_intr;
+ __u64 sample_simd_vec_reg_user;
};

/*
@@ -1020,7 +1041,15 @@ enum perf_event_type {
* } && PERF_SAMPLE_BRANCH_STACK
*
* { u64 abi; # enum perf_sample_regs_abi
- * u64 regs[weight(mask)]; } && PERF_SAMPLE_REGS_USER
+ * u64 regs[weight(mask)];
+ * struct {
+ * u16 nr_vectors; # 0 ... weight(sample_simd_vec_reg_user)
+ * u16 vector_qwords; # 0 ... sample_simd_vec_reg_qwords
+ * u16 nr_pred; # 0 ... weight(sample_simd_pred_reg_user)
+ * u16 pred_qwords; # 0 ... sample_simd_pred_reg_qwords
+ * u64 data[nr_vectors * vector_qwords + nr_pred * pred_qwords];
+ * } && (abi & PERF_SAMPLE_REGS_ABI_SIMD)
+ * } && PERF_SAMPLE_REGS_USER
*
* { u64 size;
* char data[size];
@@ -1047,7 +1076,15 @@ enum perf_event_type {
* { u64 data_src; } && PERF_SAMPLE_DATA_SRC
* { u64 transaction; } && PERF_SAMPLE_TRANSACTION
* { u64 abi; # enum perf_sample_regs_abi
- * u64 regs[weight(mask)]; } && PERF_SAMPLE_REGS_INTR
+ * u64 regs[weight(mask)];
+ * struct {
+ * u16 nr_vectors; # 0 ... weight(sample_simd_vec_reg_intr)
+ * u16 vector_qwords; # 0 ... sample_simd_vec_reg_qwords
+ * u16 nr_pred; # 0 ... weight(sample_simd_pred_reg_intr)
+ * u16 pred_qwords; # 0 ... sample_simd_pred_reg_qwords
+ * u64 data[nr_vectors * vector_qwords + nr_pred * pred_qwords];
+ * } && (abi & PERF_SAMPLE_REGS_ABI_SIMD)
+ * } && PERF_SAMPLE_REGS_INTR
* { u64 phys_addr;} && PERF_SAMPLE_PHYS_ADDR
* { u64 cgroup;} && PERF_SAMPLE_CGROUP
* { u64 data_page_size;} && PERF_SAMPLE_DATA_PAGE_SIZE

To maintain simplicity, a single field, sample_{simd|pred}_vec_reg_qwords,
is introduced to indicate register width. For example:
- sample_simd_vec_reg_qwords = 2 for XMM registers (128 bits) on x86
- sample_simd_vec_reg_qwords = 4 for YMM registers (256 bits) on x86

Four additional fields, sample_{simd|pred}_vec_reg_{intr|user}, represent
the bitmap of sampling registers. For instance, the bitmap for x86
XMM registers is 0xffff (16 XMM registers). Although users can
theoretically sample a subset of registers, the current perf-tool
implementation supports sampling all registers of each type to avoid
complexity.

A new ABI, PERF_SAMPLE_REGS_ABI_SIMD, is introduced to signal user space
tools about the presence of SIMD registers in sampling records. When this
flag is detected, tools should recognize that extra SIMD register data
follows the general register data. The layout of the extra SIMD register
data is displayed as follow.

u16 nr_vectors;
u16 vector_qwords;
u16 nr_pred;
u16 pred_qwords;
u64 data[nr_vectors * vector_qwords + nr_pred * pred_qwords];

With this patch set, sampling for the aforementioned registers is
supported on the Intel Nova Lake platform.

Examples:
$perf record -I?
available registers: AX BX CX DX SI DI BP SP IP FLAGS CS SS R8 R9 R10
R11 R12 R13 R14 R15 R16 R17 R18 R19 R20 R21 R22 R23 R24 R25 R26 R27 R28
R29 R30 R31 SSP XMM0-15 YMM0-15 ZMM0-31 OPMASK0-7

$perf record --user-regs=?
available registers: AX BX CX DX SI DI BP SP IP FLAGS CS SS R8 R9 R10
R11 R12 R13 R14 R15 R16 R17 R18 R19 R20 R21 R22 R23 R24 R25 R26 R27 R28
R29 R30 R31 SSP XMM0-15 YMM0-15 ZMM0-31 OPMASK0-7

$perf record -e branches:p -Iax,bx,r8,r16,r31,ssp,xmm,ymm,zmm,opmask -c 100000 ./test
$perf report -D

... ...
14027761992115 0xcf30 [0x8a8]: PERF_RECORD_SAMPLE(IP, 0x1): 29964/29964:
0xffffffff9f085e24 period: 100000 addr: 0
... intr regs: mask 0x18001010003 ABI 64-bit
.... AX 0xdffffc0000000000
.... BX 0xffff8882297685e8
.... R8 0x0000000000000000
.... R16 0x0000000000000000
.... R31 0x0000000000000000
.... SSP 0x0000000000000000
... SIMD ABI nr_vectors 32 vector_qwords 8 nr_pred 8 pred_qwords 1
.... ZMM [0] 0xffffffffffffffff
.... ZMM [0] 0x0000000000000001
.... ZMM [0] 0x0000000000000000
.... ZMM [0] 0x0000000000000000
.... ZMM [0] 0x0000000000000000
.... ZMM [0] 0x0000000000000000
.... ZMM [0] 0x0000000000000000
.... ZMM [0] 0x0000000000000000
.... ZMM [1] 0x003a6b6165506d56
... ...
.... ZMM [31] 0x0000000000000000
.... ZMM [31] 0x0000000000000000
.... ZMM [31] 0x0000000000000000
.... ZMM [31] 0x0000000000000000
.... ZMM [31] 0x0000000000000000
.... ZMM [31] 0x0000000000000000
.... ZMM [31] 0x0000000000000000
.... ZMM [31] 0x0000000000000000
.... OPMASK[0] 0x00000000fffffe00
.... OPMASK[1] 0x0000000000ffffff
.... OPMASK[2] 0x000000000000007f
.... OPMASK[3] 0x0000000000000000
.... OPMASK[4] 0x0000000000010080
.... OPMASK[5] 0x0000000000000000
.... OPMASK[6] 0x0000400004000000
.... OPMASK[7] 0x0000000000000000
... ...

History:
v6: https://lore.kernel.org/all/20260209072047.2180332-1-dapeng1.mi@linux.intel.com/
v5: https://lore.kernel.org/all/20251203065500.2597594-1-dapeng1.mi@linux.intel.com/
v4: https://lore.kernel.org/all/20250925061213.178796-1-dapeng1.mi@linux.intel.com/
v3: https://lore.kernel.org/lkml/20250815213435.1702022-1-kan.liang@linux.intel.com/
v2: https://lore.kernel.org/lkml/20250626195610.405379-1-kan.liang@linux.intel.com/
v1: https://lore.kernel.org/lkml/20250613134943.3186517-1-kan.liang@linux.intel.com/

Dapeng Mi (12):
perf/x86: Move hybrid PMU initialization before x86_pmu_starting_cpu()
perf/x86/intel: Avoid PEBS event on fixed counters without extended
PEBS
perf/x86/intel: Enable large PEBS sampling for XMMs
perf/x86/intel: Convert x86_perf_regs to per-cpu variables
perf: Eliminate duplicate arch-specific functions definations
x86/fpu: Ensure TIF_NEED_FPU_LOAD is set after saving FPU state
perf/x86: Enable XMM Register Sampling for Non-PEBS Events
perf/x86: Enable XMM register sampling for REGS_USER case
perf: Enhance perf_reg_validate() with simd_enabled argument
perf/x86/intel: Enable arch-PEBS based SIMD/eGPRs/SSP sampling
perf/x86: Activate back-to-back NMI detection for arch-PEBS induced
NMIs
perf/x86/intel: Add sanity check for PEBS fragment size

Kan Liang (12):
perf/x86: Use x86_perf_regs in the x86 nmi handler
perf/x86: Introduce x86-specific x86_pmu_setup_regs_data()
x86/fpu/xstate: Add xsaves_nmi() helper
perf: Move and rename has_extended_regs() for ARCH-specific use
perf: Add sampling support for SIMD registers
perf/x86: Enable XMM sampling using sample_simd_vec_reg_* fields
perf/x86: Enable YMM sampling using sample_simd_vec_reg_* fields
perf/x86: Enable ZMM sampling using sample_simd_vec_reg_* fields
perf/x86: Enable OPMASK sampling using sample_simd_pred_reg_* fields
perf/x86: Enable eGPRs sampling using sample_regs_* fields
perf/x86: Enable SSP sampling using sample_regs_* fields
perf/x86/intel: Enable PERF_PMU_CAP_SIMD_REGS capability

arch/arm/kernel/perf_regs.c | 8 +-
arch/arm64/kernel/perf_regs.c | 8 +-
arch/csky/kernel/perf_regs.c | 8 +-
arch/loongarch/kernel/perf_regs.c | 8 +-
arch/mips/kernel/perf_regs.c | 8 +-
arch/parisc/kernel/perf_regs.c | 8 +-
arch/powerpc/perf/perf_regs.c | 2 +-
arch/riscv/kernel/perf_regs.c | 8 +-
arch/s390/kernel/perf_regs.c | 2 +-
arch/x86/events/core.c | 392 +++++++++++++++++++++++++-
arch/x86/events/intel/core.c | 127 ++++++++-
arch/x86/events/intel/ds.c | 195 ++++++++++---
arch/x86/events/perf_event.h | 85 +++++-
arch/x86/include/asm/fpu/sched.h | 5 +-
arch/x86/include/asm/fpu/xstate.h | 3 +
arch/x86/include/asm/msr-index.h | 7 +
arch/x86/include/asm/perf_event.h | 38 ++-
arch/x86/include/uapi/asm/perf_regs.h | 51 ++++
arch/x86/kernel/fpu/core.c | 27 +-
arch/x86/kernel/fpu/xstate.c | 25 +-
arch/x86/kernel/perf_regs.c | 134 +++++++--
include/linux/perf_event.h | 16 ++
include/linux/perf_regs.h | 36 +--
include/uapi/linux/perf_event.h | 50 +++-
kernel/events/core.c | 138 +++++++--
tools/perf/util/header.c | 3 +-
26 files changed, 1193 insertions(+), 199 deletions(-)

--
2.34.1