From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751920Ab2AYKtu (ORCPT ); Wed, 25 Jan 2012 05:49:50 -0500 Received: from casper.infradead.org ([85.118.1.10]:56298 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751151Ab2AYKtt (ORCPT ); Wed, 25 Jan 2012 05:49:49 -0500 Subject: Re: [RFCv3 0/9] perf tool: parser generator for events parsing From: Peter Zijlstra To: Greg KH Cc: Jiri Olsa , acme@redhat.com, mingo@elte.hu, paulus@samba.org, cjashfor@linux.vnet.ibm.com, linux-kernel@vger.kernel.org In-Reply-To: <20120125005342.GA24662@kroah.com> References: <20120109152855.GA1597@m.brq.redhat.com> <1326717103-10287-1-git-send-email-jolsa@redhat.com> <1327422364.2446.75.camel@twins> <20120125005342.GA24662@kroah.com> Content-Type: text/plain; charset="UTF-8" Date: Wed, 25 Jan 2012 11:49:33 +0100 Message-ID: <1327488573.2614.59.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.32.2 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2012-01-24 at 16:53 -0800, Greg KH wrote: > Well, what's to keep someone from exploding one of those files to go > over the buffer size without knowing it? The content is known at compile time, we could put checks in. But yeah 4k isn't that much text.. > Even after reading the above link, I can't really understand what this > is being used for. As it's sysfs files, why aren't Documentation/ABI/ > files also being created with the patch explaining it all? Ah, yeah, documentation, wasn't that written in C :-) But fair enough... Anyway, the purpose is to describe the magic bits that go into perf_event_attr::config[012] for a particular pmu. Basically they're the 'hardware' bitmasks we want to export, so that userspace can deal with sane name/value pairs. > Again, if at all possible, sysfs should be one value per file. Please > NEVER create a sysfs file that requires a parser to determine what is > going on in it. It should be a simple 'read the value' type thing. The whole purpose was to drive a parser :-) Anyway, is: "config:0-7,32-35" acceptable for a single file? This means, the 'config' member of struct perf_event_attr bits 0-7,32-35 form a bitfield whose name is then given by the filename that has this content. > So yes, multiple sysfs files do make sense, the resource load should be > almost non-existant for new ones. Surely all these attribute objects take more space than a few lines of text, but ok, I guess multiple files it is.