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Message-ID: <CAP-5=fW=qZzAsmc7CKj-GGbABBgCB7KhK+Xa8K1LiUGJJBC9Hg@mail.gmail.com>
Date: Wed, 3 Dec 2025 16:24:18 -0800
From: Ian Rogers <irogers@...gle.com>
To: Dapeng Mi <dapeng1.mi@...ux.intel.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
Adrian Hunter <adrian.hunter@...el.com>, Jiri Olsa <jolsa@...nel.org>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Andi Kleen <ak@...ux.intel.com>,
Eranian Stephane <eranian@...gle.com>, Mark Rutland <mark.rutland@....com>, broonie@...nel.org,
Ravi Bangoria <ravi.bangoria@....com>, linux-kernel@...r.kernel.org,
linux-perf-users@...r.kernel.org, Zide Chen <zide.chen@...el.com>,
Falcon Thomas <thomas.falcon@...el.com>, Dapeng Mi <dapeng1.mi@...el.com>,
Xudong Hao <xudong.hao@...el.com>
Subject: Re: [Patch v5 00/19] Support SIMD/eGPRs/SSP registers sampling for perf
On Tue, Dec 2, 2025 at 10:58 PM Dapeng Mi <dapeng1.mi@...ux.intel.com> wrote:
>
> 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.
>
> @@ -543,6 +545,25 @@ struct perf_event_attr {
> __u64 sig_data;
>
> __u64 config3; /* extension of config2 */
> +
> +
> + /*
> + * 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;
> + };
> + __u32 sample_simd_pred_reg_intr;
> + __u32 sample_simd_pred_reg_user;
> + __u16 sample_simd_vec_reg_qwords;
> + __u64 sample_simd_vec_reg_intr;
> + __u64 sample_simd_vec_reg_user;
> + __u32 __reserved_4;
> };
> @@ -1016,7 +1037,15 @@ 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;
> + * u16 vector_qwords;
> + * u16 nr_pred;
> + * u16 pred_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];
> @@ -1043,7 +1072,15 @@ 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;
> + * u16 vector_qwords;
> + * u16 nr_pred;
> + * u16 pred_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
nit: It seems strange in this output to mix ranges like "XMM0-15" but
then list out "R8....R31". That said we have tests that explicitly
look for the non-range pattern:
https://web.git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/tests/shell/record.sh?h=perf-tools-next#n106
Thanks,
Ian
> $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:
> 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 (3):
> perf: Eliminate duplicate arch-specific functions definations
> perf/x86/intel: Enable arch-PEBS based SIMD/eGPRs/SSP sampling
> perf/x86: Activate back-to-back NMI detection for arch-PEBS induced
> NMIs
>
> Kan Liang (16):
> 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/x86: Add support for XMM registers in non-PEBS and REGS_USER
> 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
> perf headers: Sync with the kernel headers
> perf parse-regs: Support new SIMD sampling format
> perf regs: Enable dumping of SIMD registers
>
> 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 | 326 +++++++++++-
> arch/x86/events/intel/core.c | 117 ++++-
> arch/x86/events/intel/ds.c | 134 ++++-
> arch/x86/events/perf_event.h | 85 +++-
> 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 | 62 +++
> arch/x86/kernel/fpu/xstate.c | 25 +-
> arch/x86/kernel/perf_regs.c | 131 ++++-
> include/linux/perf_event.h | 16 +
> include/linux/perf_regs.h | 36 +-
> include/uapi/linux/perf_event.h | 45 +-
> kernel/events/core.c | 132 ++++-
> tools/arch/x86/include/uapi/asm/perf_regs.h | 62 +++
> tools/include/uapi/linux/perf_event.h | 45 +-
> tools/perf/arch/x86/util/perf_regs.c | 470 +++++++++++++++++-
> tools/perf/util/evsel.c | 47 ++
> tools/perf/util/parse-regs-options.c | 151 +++++-
> .../perf/util/perf-regs-arch/perf_regs_x86.c | 43 ++
> tools/perf/util/perf_event_attr_fprintf.c | 6 +
> tools/perf/util/perf_regs.c | 59 +++
> tools/perf/util/perf_regs.h | 11 +
> tools/perf/util/record.h | 6 +
> tools/perf/util/sample.h | 10 +
> tools/perf/util/session.c | 78 ++-
> 35 files changed, 2012 insertions(+), 193 deletions(-)
>
>
> base-commit: 9929dffce5ed7e2988e0274f4db98035508b16d9
> prerequisite-patch-id: a15bcd62a8dcd219d17489eef88b66ea5488a2a0
> --
> 2.34.1
>
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