From: yunhui cui <cuiyunhui@bytedance.com>
To: atish.patra@linux.dev, Anup Patel <anup@brainfault.org>,
Will Deacon <will@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Paul Walmsley <paul.walmsley@sifive.com>,
Palmer Dabbelt <palmer@dabbelt.com>,
Albert Ou <aou@eecs.berkeley.edu>,
Alexandre Ghiti <alex@ghiti.fr>,
linux-riscv <linux-riscv@lists.infradead.org>,
linux-arm-kernel@lists.infradead.org,
linux-perf-users@vger.kernel.org,
lkml - Kernel Mailing List <linux-kernel@vger.kernel.org>,
Atish Patra <atishp@rivosinc.com>
Subject: [REPORT] Should rdcycle be deprecated?
Date: Tue, 9 Sep 2025 11:13:35 +0800 [thread overview]
Message-ID: <CAEEQ3wmjRuC-Z1PRTw1chP40KXFksBgHu+dayjYA9KXE9Q0Cmw@mail.gmail.com> (raw)
Hi All,
1. To use rdcycle in user mode, one must first go through
perf_user_access. However, in reality, the return value of rdcycle
remains unchanged. This is because SBI_PMU_CY_IR_MASK in SBI includes
the bit corresponding to "cycle", and the kernel's pmu_sbi_stop_all()
function disables the counting of cycles.
2. Currently, some application software (e.g., DPDK) uses the rdcycle
instruction. In fact, rdcycle is affected by WFI (Wait for Interrupt)
and CPU frequency variations.
3. Some applications mainly run on server CPUs. Therefore, the
precision design of rdtime should be higher. For example, the TSC
(Time-Stamp Counter) of x86 architectures is generally around 2 GHz,
which can meet the application's requirements for timestamp precision.
4. What are the future plans for rdcycle?
Thanks,
Yunhui
reply other threads:[~2025-09-09 3:13 UTC|newest]
Thread overview: [no followups] expand[flat|nested] mbox.gz Atom feed
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CAEEQ3wmjRuC-Z1PRTw1chP40KXFksBgHu+dayjYA9KXE9Q0Cmw@mail.gmail.com \
--to=cuiyunhui@bytedance.com \
--cc=alex@ghiti.fr \
--cc=anup@brainfault.org \
--cc=aou@eecs.berkeley.edu \
--cc=atish.patra@linux.dev \
--cc=atishp@rivosinc.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-perf-users@vger.kernel.org \
--cc=linux-riscv@lists.infradead.org \
--cc=mark.rutland@arm.com \
--cc=palmer@dabbelt.com \
--cc=paul.walmsley@sifive.com \
--cc=will@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).