From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id B65D018DF80 for ; Fri, 19 Jun 2026 14:00:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781877635; cv=none; b=qWJ3OQnpB8ahQNE7KcpZ6fjJVHOAYWgA7XKGGvxabryIvMTFVpC/IAI5uLeyztgGm9vby03Lx3TaHFfK16ShpJuCb7FL6ajRiNyzWlh+C2KBohnJSsKy0Xnxb7JwLhuSKxYgi7NREH8epLYU0mSmZicTC+YzX+nFKkBwhr0Fs3w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781877635; c=relaxed/simple; bh=5OFQ9ATndI+CfKRhU1GLZ71nxhhjUHxiVn0+oHyd+Uc=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=VL1DMoUNkzRrCxNkfZ3DgWNt7i9nn4PbcHGh+ZFbmV/sORe8NrQKp+O5Q3YXT2WioJ1+AEVGrpwS5kegZLR/vZxi67ZDol224tCFGC3ObU+0yDUb0iKTS+8z3T35KJil5b/A0OrtTu00b8JRk0E5izBUIlhE6BJSSxrvYSnvXFw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=TKWENYr6; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="TKWENYr6" 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 132382923; Fri, 19 Jun 2026 07:00:28 -0700 (PDT) Received: from arm.com (usa-sjc-mx-foss1.foss.arm.com [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B49D03F763; Fri, 19 Jun 2026 07:00:29 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1781877632; bh=5OFQ9ATndI+CfKRhU1GLZ71nxhhjUHxiVn0+oHyd+Uc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=TKWENYr6DnwXdIkTUnV+13GaxlcORxcxDxA+ToU6J+hKo+VC7VpQvp9yx8p6Ob3Jb ITB11Z6ChJMlTzZfJvXUe3zzrnMn+fhtH09Vovuzihv4AP7lOi/slveAZkttTVCkMk ZbqHnQbbm/nbu7tNVta3+Rk56KurGsaz0TDOeUSM= Date: Fri, 19 Jun 2026 15:00:26 +0100 From: Catalin Marinas To: Kiryl Shutsemau Cc: Will Deacon , James Morse , Mark Rutland , Marc Zyngier , Doug Anderson , Petr Mladek , Thomas Gleixner , Andrew Morton , Baoquan He , Puranjay Mohan , Usama Arif , Breno Leitao , Julien Thierry , Lecopzer Chen , Sumit Garg , kernel-team@meta.com, kexec@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, "Kiryl Shutsemau (Meta)" Subject: Re: [PATCH v4 0/4] arm64: cross-CPU NMI via SDEI Message-ID: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Hi Kiryl, On Wed, Jun 17, 2026 at 08:20:01PM +0100, Kiryl Shutsemau wrote: > - GICv3 pseudo-NMI (interrupt priority masking). Its cost is on the > interrupt mask/unmask hot path: local_irq_enable() becomes an > ICC_PMR_EL1 write plus a synchronising barrier, and exception > entry/exit save and restore the PMR, paid on every CPU whether or not > an NMI is ever delivered. In our measurements, enabling pseudo-NMI > costs up to ~5% on real workloads, and ~66% on a syscall-in-a-loop > microbenchmark. A fleet-wide ~5% regression is not acceptable, so > these systems run with pseudo-NMI disabled. Does your firmware set ICC_CTLR_EL1.PMHE? I'd be curious to see the numbers if the DSB was omitted on the enable path. > This series adds a third delivery backend that costs nothing on the hot > path: SDEI. Firmware delivers an SDEI event into a CPU regardless of its > DAIF state, so interrupt masking stays the cheap PSTATE.DAIF operation and > the firmware round-trip is paid only at the rare moment a CPU must be > interrupted. The direction of travel is to deprecated SDEI. I wouldn't add more stuff on top of this interface. (I haven't looked at the patches yet; Marc/Mark/James are more knowledgeable than me in this area) -- Catalin