From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D31E8A55; Mon, 1 Dec 2025 00:31:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764549061; cv=none; b=cWNhsJ3UNlrSSIzSojcsSYqQEf37MjhdqAUQHaeavPTghrj9DsAhZHWq8NA0+m0Cf3gE8k1FHnkO62RxJUO1YZ/ADwNub7GQ5crIQDAhsX1i7HenVxx+JONX0V2j8DYsvVEgGYdEBwzcpognuRuhxHIb89bFgAJRp9dgX8SR82A= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764549061; c=relaxed/simple; bh=e0d1UPxi03h0AozV9+X7CmZKceGti3RSfEqjNkXsT60=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=I/v1VEXc6iLnKPZBYzTWgU9J/Kixy+W8ZYK/7XiQTNVkW0ruxbUfXKK7g0cxS89E6G6O9tlU+IBBV1RxGhJVwubczhaBP96F45GhZ3VW1wPVibXYnT4vXeSbS3PdZysoyfLVQfeKb38VWAcJE15BdBR6JWhmIbFwi2+cx4CuAeE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=RB6X1fAx; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="RB6X1fAx" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E9F1BC4CEFB; Mon, 1 Dec 2025 00:30:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1764549060; bh=e0d1UPxi03h0AozV9+X7CmZKceGti3RSfEqjNkXsT60=; h=From:To:Cc:Subject:Date:From; b=RB6X1fAxFkN/0RwTZGmdbkz4+8QbT1jD8e8apWMaI9d4uv43ofqltogWyqdZDGEV6 z46CIZya/7/1ho+ah109BI4WlUmeTUuU5dUBqWlGERjI/G+GfK5FSU+d1yy3hXfmEQ EIc4pH8HPPV//9IhYNpc2R/rnebbPdVeQvXC9nOkCNdEGXOSMo2VxUDG7vdw6eSwZ5 7EKrsjKfvJt88eTuSb7NtvZjYmkDSKy1pGOoyc+zTLAv+qGoFph6vaRyaDg5qeYP50 IoxoCesNknGQwNnF1zBdqxiSRS9Y3RaKQmmG+V4MwhdQ/hA0xMeVCY0nHaLfGrgVQZ QNU+A3Dh+uExQ== From: guoren@kernel.org To: paul.walmsley@sifive.com, palmer@dabbelt.com, guoren@kernel.org, leobras@redhat.com, ajones@ventanamicro.com, anup@brainfault.org, atish.patra@linux.dev, corbet@lwn.net Cc: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, kvm-riscv@lists.infradead.org, kvm@vger.kernel.org, linux-doc@vger.kernel.org Subject: [RFC PATCH V3 0/4] RISC-V: Add PARAVIRT_SPINLOCKS support Date: Sun, 30 Nov 2025 19:30:37 -0500 Message-Id: <20251201003041.695081-1-guoren@kernel.org> X-Mailer: git-send-email 2.40.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: "Guo Ren (Alibaba DAMO Academy)" Paravirtualized spinlocks allow a unfair qspinlock to replace the ticket-lock or native fair qspinlock implementation with something virtualization-friendly, for example, halt the virtual CPU rather than spinning. You could observe the paravirt qspinlock internal work situation with /sys/kernel/debug/tracing/trace: ls /sys/kernel/debug/tracing/events/paravirt/ enable filter pv_kick pv_wait echo 1 > /sys/kernel/debug/tracing/events/paravirt/enable cat /sys/kernel/debug/tracing/trace entries-in-buffer/entries-written: 33927/33927 #P:12 _-----=> irqs-off/BH-disabled / _----=> need-resched | / _---=> hardirq/softirq || / _--=> preempt-depth ||| / _-=> migrate-disable |||| / delay TASK-PID CPU# ||||| TIMESTAMP FUNCTION | | | ||||| | | sh-100 [001] d..2. 28.312294: pv_wait: cpu 1 out of wfi -0 [000] d.h4. 28.322030: pv_kick: cpu 0 kick target cpu 1 sh-100 [001] d..2. 30.982631: pv_wait: cpu 1 out of wfi -0 [000] d.h4. 30.993289: pv_kick: cpu 0 kick target cpu 1 sh-100 [002] d..2. 44.987573: pv_wait: cpu 2 out of wfi -0 [000] d.h4. 44.989000: pv_kick: cpu 0 kick target cpu 2 -0 [003] d.s3. 51.593978: pv_kick: cpu 3 kick target cpu 4 rcu_sched-15 [004] d..2. 51.595192: pv_wait: cpu 4 out of wfi lock_torture_wr-115 [004] ...2. 52.656482: pv_kick: cpu 4 kick target cpu 2 lock_torture_wr-113 [002] d..2. 52.659146: pv_wait: cpu 2 out of wfi lock_torture_wr-114 [008] d..2. 52.659507: pv_wait: cpu 8 out of wfi lock_torture_wr-114 [008] d..2. 52.663503: pv_wait: cpu 8 out of wfi lock_torture_wr-113 [002] ...2. 52.666128: pv_kick: cpu 2 kick target cpu 8 lock_torture_wr-114 [008] d..2. 52.667261: pv_wait: cpu 8 out of wfi lock_torture_wr-114 [009] .n.2. 53.141515: pv_kick: cpu 9 kick target cpu 11 lock_torture_wr-113 [002] d..2. 53.143339: pv_wait: cpu 2 out of wfi lock_torture_wr-116 [007] d..2. 53.143412: pv_wait: cpu 7 out of wfi lock_torture_wr-118 [000] d..2. 53.143457: pv_wait: cpu 0 out of wfi lock_torture_wr-115 [008] d..2. 53.143481: pv_wait: cpu 8 out of wfi lock_torture_wr-117 [011] d..2. 53.143522: pv_wait: cpu 11 out of wfi lock_torture_wr-117 [011] ...2. 53.143987: pv_kick: cpu 11 kick target cpu 8 lock_torture_wr-115 [008] ...2. 53.144269: pv_kick: cpu 8 kick target cpu 7 This series is split from [1]. The newest discussion is at [2]. [1]: https://lore.kernel.org/linux-riscv/20231225125847.2778638-1-guoren@kernel.org/ [2]: https://lists.riscv.org/g/tech-prs/message/1211 Changelog: v3: - Rebase on linux-6.18-rc7. - Simplify nopvspin usage. v2: https://lore.kernel.org/linux-riscv/20241227011011.2331381-1-guoren@kernel.org/ - Add RFC tag. - Using new SBI_EXT_PVLOCK ID. - Add virt_spin_lock support. - Add nopvspin support. v1: https://lore.kernel.org/linux-riscv/20241222033917.1754495-1-guoren@kernel.org/ Guo Ren (Alibaba DAMO Academy) (4): RISC-V: paravirt: Add pvqspinlock KVM backend RISC-V: paravirt: Add pvqspinlock frontend RISC-V: paravirt: pvqspinlock: Add trace point for pv_kick/wait RISC-V: paravirt: Support nopvspin to disable PARAVIRT_SPINLOCKS .../admin-guide/kernel-parameters.txt | 2 +- arch/riscv/Kconfig | 12 +++ arch/riscv/include/asm/Kbuild | 1 - arch/riscv/include/asm/kvm_vcpu_sbi.h | 1 + arch/riscv/include/asm/qspinlock.h | 59 +++++++++++++ arch/riscv/include/asm/qspinlock_paravirt.h | 28 +++++++ arch/riscv/include/asm/sbi.h | 5 ++ arch/riscv/include/uapi/asm/kvm.h | 1 + arch/riscv/kernel/Makefile | 2 + arch/riscv/kernel/qspinlock_paravirt.c | 84 +++++++++++++++++++ arch/riscv/kernel/setup.c | 5 ++ .../kernel/trace_events_filter_paravirt.h | 60 +++++++++++++ arch/riscv/kvm/Makefile | 1 + arch/riscv/kvm/vcpu_sbi.c | 4 + arch/riscv/kvm/vcpu_sbi_pvlock.c | 57 +++++++++++++ 15 files changed, 320 insertions(+), 2 deletions(-) create mode 100644 arch/riscv/include/asm/qspinlock.h create mode 100644 arch/riscv/include/asm/qspinlock_paravirt.h create mode 100644 arch/riscv/kernel/qspinlock_paravirt.c create mode 100644 arch/riscv/kernel/trace_events_filter_paravirt.h create mode 100644 arch/riscv/kvm/vcpu_sbi_pvlock.c -- 2.40.1