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 871616F2E6; Thu, 30 May 2024 10:03:10 +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=1717063392; cv=none; b=gpxsuFhN3VNKNxwno0XDzVoZnn0HfK1IH1Ha3IfI+5RqRq8YekFTI+/MO3Aji/Hao+qWPls52Z6eTRDtuAZD2d0RZY7qel615WqwglfyD3fZo+2vU3i0PK6MriE2IyKNezqjR3w9J15lk4SaO/hjyO4eK+AFZj6mpvYbfpfn7Gc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1717063392; c=relaxed/simple; bh=OUn7iuxuw7dEQyjT1Zqqm9Q0bZLJ5YwLkhbMQ3hWXmI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=J1suG7CdT506IGKMWThNElPFffCMMTGuL81AoDFLkYmQZIPREeLVFWdRUmrYfLe8z4V0chN9grZYAlCL77lbjbvLUH+msB9yeg3Dk/1H5jAjULe8DF4ibLTVwSk6DVA/s0s10Pzq8nooG9Ak6RBaKGqUYKy/0syDmHfULDKWecY= 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; 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 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 2826E339; Thu, 30 May 2024 03:03:34 -0700 (PDT) Received: from [192.168.1.100] (usa-sjc-mx-foss1.foss.arm.com [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 317CE3F792; Thu, 30 May 2024 03:03:08 -0700 (PDT) Message-ID: <5f8fdfd2-a4f9-4fde-ad24-3b76231e61c8@arm.com> Date: Thu, 30 May 2024 11:03:10 +0100 Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V17 0/9] arm64/perf: Enable branch stack sampling To: Anshuman Khandual Cc: Mark Brown , Rob Herring , Marc Zyngier , Suzuki Poulose , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , linux-perf-users@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, will@kernel.org, catalin.marinas@arm.com, mark.rutland@arm.com References: <20240405024639.1179064-1-anshuman.khandual@arm.com> Content-Language: en-US From: James Clark In-Reply-To: <20240405024639.1179064-1-anshuman.khandual@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 05/04/2024 03:46, Anshuman Khandual wrote: > This series enables perf branch stack sampling support on arm64 platform > via a new arch feature called Branch Record Buffer Extension (BRBE). All > the relevant register definitions could be accessed here. > > https://developer.arm.com/documentation/ddi0601/2021-12/AArch64-Registers > > This series applies on 6.9-rc2. > > Also this series is being hosted below for quick access, review and test. > > https://git.gitlab.arm.com/linux-arm/linux-anshuman.git (brbe_v17) > > There are still some open questions regarding handling multiple perf events > with different privilege branch filters getting on the same PMU, supporting > guest branch stack tracing from the host etc. Finally also looking for some > suggestions regarding supporting BRBE inside the guest. The series has been > re-organized completely as suggested earlier. For guest support I'm still of this opinion: * No support for the host looking into guests (the addresses don't make sense anyway without also running Perf record in the guest) * Save and restore the host buffer and registers on guest switch (if it was ever used by either host or guest) * Let the guest do whatever it wants with BRBE without any virtualisation Merging this with the current PMU virtualistion stuff seems like a lot of work for no use case (host looking into guests). Having said that, it might not even be worth discussing on this patchset apart from "no guest support", and we can do it later to avoid confusion that it's being proposed for this version. James