Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751919AbaKQJdH (ORCPT ); Mon, 17 Nov 2014 04:33:07 -0500 Received: from mga01.intel.com ([192.55.52.88]:55030 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751300AbaKQJdF convert rfc822-to-8bit (ORCPT ); Mon, 17 Nov 2014 04:33:05 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.97,862,1389772800"; d="scan'208";a="417516430" From: "Metzger, Markus T" To: Alexander Shishkin , Peter Zijlstra CC: Ingo Molnar , "linux-kernel@vger.kernel.org" , Robert Richter , "Frederic Weisbecker" , Mike Galbraith , "Paul Mackerras" , Stephane Eranian , "Andi Kleen" , "Liang, Kan" , "Hunter, Adrian" , "mathieu.poirier@linaro.org" , "acme@infradead.org" , Peter Zijlstra Subject: RE: [PATCH v8 02/14] perf: Add AUX area to ring buffer for raw data streams Thread-Topic: [PATCH v8 02/14] perf: Add AUX area to ring buffer for raw data streams Thread-Index: AQHQABEn9YCSj49H5EmAjQeZXjmYpZxkkV6g Date: Mon, 17 Nov 2014 09:33:00 +0000 Message-ID: References: <1415972627-37514-1-git-send-email-alexander.shishkin@linux.intel.com> <1415972627-37514-3-git-send-email-alexander.shishkin@linux.intel.com> In-Reply-To: <1415972627-37514-3-git-send-email-alexander.shishkin@linux.intel.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [163.33.239.180] Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > -----Original Message----- > From: Alexander Shishkin [mailto:alexander.shishkin@linux.intel.com] > Sent: Friday, November 14, 2014 2:44 PM > To: Peter Zijlstra > Cc: Ingo Molnar; linux-kernel@vger.kernel.org; Robert Richter; Frederic > Weisbecker; Mike Galbraith; Paul Mackerras; Stephane Eranian; Andi Kleen; > Liang, Kan; Hunter, Adrian; Metzger, Markus T; mathieu.poirier@linaro.org; > acme@infradead.org; Peter Zijlstra; Alexander Shishkin > Subject: [PATCH v8 02/14] perf: Add AUX area to ring buffer for raw data > streams > > From: Peter Zijlstra > > This patch introduces "AUX space" in the perf mmap buffer, intended for > exporting high bandwidth data streams to userspace, such as instruction > flow traces. > > AUX space is a ring buffer, defined by aux_{offset,size} fields in the > user_page structure, and read/write pointers aux_{head,tail}, which abide > by the same rules as data_* counterparts of the main perf buffer. > > In order to allocate/mmap AUX, userspace needs to set up aux_offset to > such an offset that will be greater than data_offset+data_size and > aux_size to be the desired buffer size. Both need to be page aligned. > Then, same aux_offset and aux_size should be passed to mmap() call and > if everything adds up, you should have an AUX buffer as a result. Why would userspace need to fill in aux_offset and aux_size? Can't the kernel do this when userspace mmaps the aux buffer like it does for the respective data_* fields? How would userspace fill in those fields if it mapped the data buffer read-only? Regards, Markus. Intel GmbH Dornacher Strasse 1 85622 Feldkirchen/Muenchen, Deutschland Sitz der Gesellschaft: Feldkirchen bei Muenchen Geschaeftsfuehrer: Christian Lamprechter, Hannes Schwaderer, Douglas Lusk Registergericht: Muenchen HRB 47456 Ust.-IdNr./VAT Registration No.: DE129385895 Citibank Frankfurt a.M. (BLZ 502 109 00) 600119052 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/