linux-kernel - Re: [Patch v5 00/19] Support SIMD/eGPRs/SSP registers sampling for perf

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Message-ID: <e796ca6f-e031-4d9f-876e-e297f9623715@linux.intel.com>
Date: Tue, 16 Dec 2025 14:59:46 +0800
From: "Mi, Dapeng" <dapeng1.mi@...ux.intel.com>
To: Ravi Bangoria <ravi.bangoria@....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>, Ian Rogers <irogers@...gle.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,
 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 12/16/2025 12:42 PM, Ravi Bangoria wrote:
> Hi Dapeng,
>
>> While the hardware solution remains preferable due to its lower
>> overhead and higher accuracy, this software approach provides a
>> viable alternative.
> Lower accuracy in the software approach is due to the delay in an NMI
> delivery which will make the SIMD data misaligned a bit? Something like:
>
>    insn1
>    insn2  -> Overflow. RIP, GPRs captured by PEBS and NMI triggered
>    insn3
>    insn4
>    insn5  -> NMI delivered here, so SIMD regs are captured here?
>    insn6
>
> Am I interpreting it correctly?

Yes, there is always a delay with software-based (specifically PMI-based)
sampling. Hardware-based sampling like PEBS is preferable when available.


>
> Thanks,
> Ravi