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From: Atish Patra <atishp@atishpatra.org>
To: "Rémi Denis-Courmont" <remi@remlab.net>
Cc: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	 Aurelien Jarno <aurelien@aurel32.net>,
	Mathieu Malaterre <malat@debian.org>,
	 Jan Newger <jannewger@google.com>
Subject: Re: [PATCH v4 00/10] riscv: Allow userspace to directly access perf counters
Date: Wed, 19 Jul 2023 10:14:36 -0700	[thread overview]
Message-ID: <CAOnJCUKCx0Jh1igZytKAYePhhUBt=x5ANCVx4FRTbLtxGkyowA@mail.gmail.com> (raw)
In-Reply-To: <5951331.lOV4Wx5bFT@basile.remlab.net>

On Wed, Jul 19, 2023 at 7:46 AM Rémi Denis-Courmont <remi@remlab.net> wrote:
>
> Le keskiviikkona 19. heinäkuuta 2023, 1.48.49 EEST Atish Patra a écrit :
> > > Isn't RDTIM susceptible to interference from power management and CPU
> > > frequency scaling? I suppose that RDCYCLE may behave differently depending
> > > on PM in *some* designs, but that would still be way better than RDTIME
> > > for the purpose.
> >
> > Yes. But that's what it is probably using for other ISAs ?
>
> At least on AArch64, it is using either Linux perf cycle counter, or if that
> is disabled at build time, the raw PMU cycle counter - which obviously leads
> to SIGILL on Linux, just like this MR would do with RDCYCLE.
>

Good to know. Thanks for the clarification.

> Again, I do not *personally* have objections to disabling RDCYCLE for
> userspace (somebody else does, but that's neither my nor your problem). I do
> have objections to the wording of some of the commit messages though.
>

Completely agreed. We will update the commit text with more clarification in v5.

> > My point was it should just do whatever it does for other ISA. RISC-V is no
> > special in that regard.
>
> Sure. My point is that RDTIME may be great for, so to say, system-level
> benchmarks. For FFmpeg that could something like how long it takes to
> transcode a video. But it doesn't seem to make much sense for
> microbenchmarking of single threaded tightly optimised loops, as opposed to
> RDCYCLE (or a wrapper for RDCYCLE).
>
> --
> Rémi Denis-Courmont
> http://www.remlab.net/
>
>
>


-- 
Regards,
Atish

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  reply	other threads:[~2023-07-19 17:15 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-07-03 12:46 [PATCH v4 00/10] riscv: Allow userspace to directly access perf counters Alexandre Ghiti
2023-07-03 12:46 ` [PATCH v4 01/10] perf: Fix wrong comment about default event_idx Alexandre Ghiti
2023-07-03 12:46 ` [PATCH v4 02/10] include: riscv: Fix wrong include guard in riscv_pmu.h Alexandre Ghiti
2023-07-03 12:46 ` [PATCH v4 03/10] riscv: Make legacy counter enum match the HW numbering Alexandre Ghiti
2023-07-14  8:01   ` Atish Patra
2023-07-03 12:46 ` [PATCH v4 04/10] drivers: perf: Rename riscv pmu sbi driver Alexandre Ghiti
2023-07-14  8:01   ` Atish Patra
2023-07-03 12:46 ` [PATCH v4 05/10] riscv: Prepare for user-space perf event mmap support Alexandre Ghiti
2023-07-14  8:03   ` Atish Patra
2023-07-03 12:46 ` [PATCH v4 06/10] drivers: perf: Implement perf event mmap support in the legacy backend Alexandre Ghiti
2023-07-14  8:03   ` Atish Patra
2023-07-03 12:46 ` [PATCH v4 07/10] drivers: perf: Implement perf event mmap support in the SBI backend Alexandre Ghiti
2023-07-14  8:46   ` Atish Patra
2023-07-20  8:36     ` Alexandre Ghiti
2023-07-03 12:46 ` [PATCH v4 08/10] Documentation: admin-guide: Add riscv sysctl_perf_user_access Alexandre Ghiti
2023-07-03 13:03   ` Andrew Jones
2023-07-04 12:28   ` Vince Weaver
2023-07-14  8:50   ` Atish Patra
2023-07-03 12:46 ` [PATCH v4 09/10] tools: lib: perf: Implement riscv mmap support Alexandre Ghiti
2023-07-14  9:29   ` Atish Patra
2023-07-03 12:46 ` [PATCH v4 10/10] perf: tests: Adapt mmap-basic.c for riscv Alexandre Ghiti
2023-07-14  9:29   ` Atish Patra
2023-07-14  9:07 ` [PATCH v4 00/10] riscv: Allow userspace to directly access perf counters Atish Patra
2023-07-17 13:35 ` Rémi Denis-Courmont
2023-07-17 23:22   ` Atish Patra
2023-07-18 17:06     ` Rémi Denis-Courmont
2023-07-18 18:45       ` Atish Patra
2023-07-18 19:04         ` Rémi Denis-Courmont
2023-07-18 22:48           ` Atish Patra
2023-07-19 14:45             ` Rémi Denis-Courmont
2023-07-19 17:14               ` Atish Patra [this message]
2023-07-20  9:13                 ` Alexandre Ghiti
2023-07-27 14:14 Alexandre Ghiti

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