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

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Message-ID: <c2892e7a-65c4-4744-a611-6fc3c1d37cd3@amd.com>
Date: Tue, 16 Dec 2025 10:12:35 +0530
From: Ravi Bangoria <ravi.bangoria@....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>, 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>, Ravi Bangoria <ravi.bangoria@....com>
Subject: Re: [Patch v5 00/19] Support SIMD/eGPRs/SSP registers sampling for
 perf

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?

Thanks,
Ravi