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a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1699461234; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=OIGc9bwNr+0t4jI3RbE7D5RwuTZ4bijPocpAhuHl4P4=; b=TjNJBuiCD7bZKxQGMdgRapwRik2d90Ys5QS77BFckvWafS/SH1bRiQ8ggAj8lpfHcEqSY6 WQJTdkW1hM54on8Ek5H7h3x+bPwjyKIGntU3YxG9weXzJTs+Jy89XRDYwCG9h6jdkrOUUq krk0HY6cbEFL9aA6BuEmlk+fT+VjvbM= Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 3797C1476; Wed, 8 Nov 2023 08:34:36 -0800 (PST) Received: from FVFF77S0Q05N (unknown [10.57.37.113]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 7B8773F64C; Wed, 8 Nov 2023 08:33:46 -0800 (PST) Date: Wed, 8 Nov 2023 16:33:43 +0000 From: Mark Rutland To: Ankur Arora Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de, peterz@infradead.org, torvalds@linux-foundation.org, paulmck@kernel.org, linux-mm@kvack.org, x86@kernel.org, akpm@linux-foundation.org, luto@kernel.org, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, willy@infradead.org, mgorman@suse.de, jon.grimm@amd.com, bharata@amd.com, raghavendra.kt@amd.com, boris.ostrovsky@oracle.com, konrad.wilk@oracle.com, jgross@suse.com, andrew.cooper3@citrix.com, mingo@kernel.org, bristot@kernel.org, mathieu.desnoyers@efficios.com, geert@linux-m68k.org, glaubitz@physik.fu-berlin.de, anton.ivanov@cambridgegreys.com, mattst88@gmail.com, krypton@ulrich-teichert.org, rostedt@goodmis.org, David.Laight@aculab.com, richard@nod.at, mjguzik@gmail.com Subject: Re: [RFC PATCH 00/86] Make the kernel preemptible Message-ID: References: <20231107215742.363031-1-ankur.a.arora@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20231107215742.363031-1-ankur.a.arora@oracle.com> X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 49E6C40002 X-Stat-Signature: bnn5hcxiftopfzwnhfd8psw5c9soie9i X-HE-Tag: 1699461234-608504 X-HE-Meta: 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 oHN+7qeV 9UgGWFbeZNFyVX74aYb5Bg+YQdWXJpsfh7jKTmm5h+9ad764/tztwKghsriv32z3Swlq59ORl8+91etrsBz/ReOGraXBnsD5SlbDoKOykTHZEiTc= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Nov 07, 2023 at 01:56:46PM -0800, Ankur Arora wrote: > What's broken: > - ARCH_NO_PREEMPT (See patch-45 "preempt: ARCH_NO_PREEMPT only preempts > lazily") > - Non-x86 architectures. It's trivial to support other archs (only need > to add TIF_NEED_RESCHED_LAZY) but wanted to hold off until I got some > comments on the series. > (From some testing on arm64, didn't find any surprises.) When you say "testing on arm64, didn't find any surprises", I assume you mean with an additional patch adding TIF_NEED_RESCHED_LAZY? Applying this series as-is atop v6.6-rc7 and building defconfig (with GCC 13.2.0) blows up with: | In file included from ./arch/arm64/include/asm/preempt.h:5, | from ./include/linux/preempt.h:79, | from ./include/linux/spinlock.h:56, | from ./include/linux/mmzone.h:8, | from ./include/linux/gfp.h:7, | from ./include/linux/slab.h:16, | from ./include/linux/resource_ext.h:11, | from ./include/linux/acpi.h:13, | from ./include/acpi/apei.h:9, | from ./include/acpi/ghes.h:5, | from ./include/linux/arm_sdei.h:8, | from arch/arm64/kernel/asm-offsets.c:10: | ./include/linux/thread_info.h:63:2: error: #error "Arch needs to define TIF_NEED_RESCHED_LAZY" | 63 | #error "Arch needs to define TIF_NEED_RESCHED_LAZY" | | ^~~~~ | ./include/linux/thread_info.h:66:42: error: 'TIF_NEED_RESCHED_LAZY' undeclared here (not in a function); did you mean 'TIF_NEED_RESCHED'? | 66 | #define TIF_NEED_RESCHED_LAZY_OFFSET (TIF_NEED_RESCHED_LAZY - TIF_NEED_RESCHED) | | ^~~~~~~~~~~~~~~~~~~~~ | ./include/linux/thread_info.h:70:24: note: in expansion of macro 'TIF_NEED_RESCHED_LAZY_OFFSET' | 70 | RESCHED_lazy = TIF_NEED_RESCHED_LAZY_OFFSET, | | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~ | make[2]: *** [scripts/Makefile.build:116: arch/arm64/kernel/asm-offsets.s] Error 1 | make[1]: *** [/home/mark/src/linux/Makefile:1202: prepare0] Error 2 | make: *** [Makefile:234: __sub-make] Error 2 Note that since arm64 doesn't use the generic entry code, that also requires changes to arm64_preempt_schedule_irq() in arch/arm64/kernel/entry-common.c, to handle TIF_NEED_RESCHED_LAZY. > - ftrace support for need-resched-lazy is incomplete What exactly do we need for ftrace here? Thanks, Mark.