From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (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 C2C2B36337A for ; Thu, 30 Oct 2025 15:28:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761838085; cv=none; b=K10sjsG1mi8iyZRJcs3kuQ6eYaYk6sHQ8pSNOyu9zCZm4COvFybrmTC/A2yIHRpCBcVAyOf3vnUzqy9z/XMHbEJKCYYdRGFfY59njeWBeuXpc4JwaoIRVXBb6axI7w8euqC2ehXD+T57COA/vMluKlYb+ecqzneD/64i0fYvkUc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761838085; c=relaxed/simple; bh=+H/TWInAyePBeiEAFJhr3RPDJ0H39GlE+N/+IuKxDU0=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=rB8fAiPK80WwW7T+vIB8x+mxM3a5EJ2ZRRs49vFShFr7e9L7wEHVNvMXpr3hEG34boJ/SjshLRLlApsLykVMEY+quZpI+X2u5ahv9vg1AWvx8+bzgRGy7Ob3iXneDnpHih5Qjj0pm3sJ9NJEWUDmzdbDkzyY0tn23kyiwejeI0c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=mUWdCq7c; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=zb46iSxJ; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="mUWdCq7c"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="zb46iSxJ" 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> Precedence: bulk X-Mailing-List: linux-rt-devel@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: 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