From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: [PATCH v3 50/51] cpuidle: Comments about noinstr/__cpuidle Date: Thu, 12 Jan 2023 20:44:04 +0100 Message-ID: <20230112195542.397238052@infradead.org> References: <20230112194314.845371875@infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: DKIM-Filter: OpenDKIM Filter v2.11.0 smtp2.osuosl.org 1CC95411AA DKIM-Filter: OpenDKIM Filter v2.11.0 smtp2.osuosl.org 33B8F415A0 DKIM-Filter: OpenDKIM Filter v2.11.0 smtp1.osuosl.org 7D71781FE3 DKIM-Filter: OpenDKIM Filter v2.11.0 smtp1.osuosl.org 3E57F81F84 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=Content-Type:MIME-Version:References: Subject:Cc:To:From:Date:Message-ID:Sender:Reply-To:Content-Transfer-Encoding: Content-ID:Content-Description:In-Reply-To; bh=Un035BTYhsjREpZ4dpy/MHkkoifcKtLiH3nYidAuKL8=; b=Cm0cZvx68fOfy3spcfZv1mTyVN I+8nrlfsPTd1YX3ddHPT1tHDaXW6BjutPk9wWpEkW/bLt/CWl0wIYVqUtY/RdgLL1CXyaqx22TN13 FVZ1Pu0U/vSbCFKDZV31A7dnMTEMlJVmC5JGl3kdM1NWuU5ROH7eP9w1vfRDaocn4JsSLc4YrPw5Q 92CcZo9NDx6pgppJhIre9PG6+hEZcTjM22p8n4v6T0CGJXpMaxOqy0BIl6Hi1HTM4//PS/Q9GRA+r r+JvkRTeh7iePDi9/CdHQ2TT4CowIVH97n1vCAGs/Zkz6o47jhi7eL2nyxXG48k7aP4oDQHY9NYIK bJ7NrLVg==; List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" To: peterz@infradead.org Cc: juri.lelli@redhat.com, rafael@kernel.org, catalin.marinas@arm.com, linus.walleij@linaro.org, nsekhar@ti.com, bsegall@google.com, guoren@kernel.org, pavel@ucw.cz, agordeev@linux.ibm.com, linux-arch@vger.kernel.org, linux-samsung-soc@vger.kernel.org, vincent.guittot@linaro.org, mpe@ellerman.id.au, chenhuacai@kernel.org, christophe.leroy@csgroup.eu, linux-acpi@vger.kernel.org, agross@kernel.org, geert@linux-m68k.org, linux-imx@nxp.com, vgupta@kernel.org, mattst88@gmail.com, mturquette@baylibre.com, sammy@sammy.net, pmladek@suse.com, linux-pm@vger.kernel.org, Sascha Hauer , linux-um@lists.infradead.org, npiggin@gmail.com, tglx@linutronix.de, linux-omap@vger.kernel.org, dietmar.eggemann@arm.com, andreyknvl@gmail.com, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, senozhatsky@chromium.org, svens@linux.ibm.com Add a few words on noinstr / __cpuidle usage. Signed-off-by: Peter Zijlstra (Intel) --- drivers/cpuidle/cpuidle.c | 12 ++++++++++++ include/linux/compiler_types.h | 10 ++++++++++ 2 files changed, 22 insertions(+) --- a/drivers/cpuidle/cpuidle.c +++ b/drivers/cpuidle/cpuidle.c @@ -252,6 +252,18 @@ noinstr int cpuidle_enter_state(struct c instrumentation_begin(); } + /* + * NOTE!! + * + * For cpuidle_state::enter() methods that do *NOT* set + * CPUIDLE_FLAG_RCU_IDLE RCU will be disabled here and these functions + * must be marked either noinstr or __cpuidle. + * + * For cpuidle_state::enter() methods that *DO* set + * CPUIDLE_FLAG_RCU_IDLE this isn't required, but they must mark the + * function calling ct_cpuidle_enter() as noinstr/__cpuidle and all + * functions called within the RCU-idle region. + */ entered_state = target_state->enter(dev, drv, index); if (WARN_ONCE(!irqs_disabled(), "%ps leaked IRQ state", target_state->enter)) --- a/include/linux/compiler_types.h +++ b/include/linux/compiler_types.h @@ -233,6 +233,16 @@ struct ftrace_likely_data { #define noinstr __noinstr_section(".noinstr.text") +/* + * The __cpuidle section is used twofold: + * + * 1) the original use -- identifying if a CPU is 'stuck' in idle state based + * on it's instruction pointer. See cpu_in_idle(). + * + * 2) supressing instrumentation around where cpuidle disables RCU; where the + * function isn't strictly required for #1, this is interchangeable with + * noinstr. + */ #define __cpuidle __noinstr_section(".cpuidle.text") #endif /* __KERNEL__ */