From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 2393ECCF9E3 for ; Thu, 30 Oct 2025 15:28:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=XcZmBDUJk7yw41e2osOtFQYA59+nZfoqavQZwKrx8SU=; b=kUqt1Hns2VfMzXG5fnzuZgCJq+ xZKlLwsmdFw7iLHQm5sP14x1g77q5Xj/hG5wjJcuJKNj3J4HB5X5v+2DslFuQwhmLxe3oF0WbWIDn BZiUEYUF6tLEotESfihXNTNkI9eEH0jakYrg83ans4gD8cXzfMhS+dXnpuybFisD0LyWVyTaASlwD t7qGKOh31B9PeDC6WuWVhoSqzLsftviSMXthtb5bfPU/CaOCooRPXvaRiWVokOl3EES5uDsCAodRN uoiTVyg9oxMI472Ux+hj2dkNBdfQ9ubGrtTlAUNp7OlzWz9F1pKKAczI1HVI01DjJvq3rQnkVWWvc YNo4Olyw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vEUZK-00000004NmI-3JWM; Thu, 30 Oct 2025 15:28:06 +0000 Received: from galois.linutronix.de ([193.142.43.55]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1vEUZH-00000004Nlr-3zMu for linux-arm-kernel@lists.infradead.org; Thu, 30 Oct 2025 15:28:05 +0000 Date: Thu, 30 Oct 2025 16:28:00 +0100 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1761838082; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=XcZmBDUJk7yw41e2osOtFQYA59+nZfoqavQZwKrx8SU=; b=mUWdCq7c+05S92Z6e3ycQap5GG7kv30irDPESS3zUYv5LZGe7HhqHaUMNrlwONd33psUke D5+1VvUj8ejnw9gyvQ+qOWQZvr0WbTRysFttiLkBTWMRczshO0ubWTEMrQgs0hKlagMPKU cPM8AYLlwviqdfPTYH1gHK7sOptPMkuIBRYojp4P5uKhpK1gE+S6KlyXrlK4Y+Ar1eueO0 8qXcCGD/hrVeABPAXazUN398ZtWm5LbCdHLHe/jQu+YuxppyfA+yKuVzCfoDLriiDMz4S6 Rqu8PxIB8v9CVRzPTCbvPTGEzl4D1ohGAN58AuP+9ks+ssgfkx0KJ47WnFvUFA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1761838082; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=XcZmBDUJk7yw41e2osOtFQYA59+nZfoqavQZwKrx8SU=; b=zb46iSxJzjaqi0J3/h4ZeZvlpftP3P6uGPFVE+TMicvvCPwsPjZkdtL4z1LgsFzylToKqK ooHg9L9VKk6q9LBA== From: Sebastian Andrzej Siewior To: Arnd Bergmann Cc: linux-arm-kernel@lists.infradead.org, linux-rt-devel@lists.linux.dev, Russell King , Xie Yuanbin , Thomas Gleixner Subject: Re: [PATCH 4/5] ARM: Disable jump-label on PREEMPT_RT. Message-ID: <20251030152800.9LD5D2GP@linutronix.de> References: <20251029155918.503060-1-bigeasy@linutronix.de> <20251029155918.503060-5-bigeasy@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20251030_082804_150244_75DEAF94 X-CRM114-Status: GOOD ( 23.17 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2025-10-30 16:24:16 [+0100], Arnd Bergmann wrote: > On Wed, Oct 29, 2025, at 16:59, Sebastian Andrzej Siewior wrote: > > From: Thomas Gleixner > > > > jump-labels are used to efficiently switch between two possible code > > paths. To achieve this, stop_machine() is used to keep the CPU in a > > known state while the opcode is modified. The usage of stop_machine() > > here leads to large latency spikes which can be observed on PREEMPT_RT. > > > > Jump labels may change the target during runtime and are not restricted > > to debug or "configuration/ setup" part of a PREEMPT_RT system where > > high latencies could be defined as acceptable. > > > > Disable jump-label support on a PREEMPT_RT system. > > > > [bigeasy: Patch description.] > > > > Signed-off-by: Thomas Gleixner > > Signed-off-by: Sebastian Andrzej Siewior > > --- > > arch/arm/Kconfig | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig > > index 864a14a434b08..99c9b1c320af8 100644 > > --- a/arch/arm/Kconfig > > +++ b/arch/arm/Kconfig > > @@ -80,7 +80,7 @@ config ARM > > select HAS_IOPORT > > select HAVE_ARCH_AUDITSYSCALL if AEABI && !OABI_COMPAT > > select HAVE_ARCH_BITREVERSE if (CPU_32v7M || CPU_32v7) && !CPU_32v6 > > - select HAVE_ARCH_JUMP_LABEL if !XIP_KERNEL && !CPU_ENDIAN_BE32 && MMU > > + select HAVE_ARCH_JUMP_LABEL if !XIP_KERNEL && !CPU_ENDIAN_BE32 && MMU > > && !PREEMPT_RT > > I posted a slightly different version last year, which optimizes > the uniprocessor version and has a little more information > in the changelog: > > https://lore.kernel.org/all/20241210160556.2341497-2-arnd@kernel.org/ This actually slipped my mind but I was fine with it according the link. So let me replace this, too. > Arnd Sebastian