Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756933AbbGQMaL (ORCPT ); Fri, 17 Jul 2015 08:30:11 -0400 Received: from szxga01-in.huawei.com ([58.251.152.64]:7053 "EHLO szxga01-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754809AbbGQMaJ (ORCPT ); Fri, 17 Jul 2015 08:30:09 -0400 Message-ID: <55A8F4BF.3020902@huawei.com> Date: Fri, 17 Jul 2015 20:27:43 +0800 From: "Wangnan (F)" User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0 MIME-Version: 1.0 To: Peter Zijlstra CC: kaixu xia , , , , , , , , , Subject: Re: [RFC PATCH 5/6] bpf: Implement function bpf_read_pmu() that get the selected hardware PMU conuter References: <1437129816-13176-1-git-send-email-xiakaixu@huawei.com> <1437129816-13176-6-git-send-email-xiakaixu@huawei.com> <20150717110541.GJ12596@twins.programming.kicks-ass.net> <55A8E703.70306@huawei.com> <20150717113924.GD19282@twins.programming.kicks-ass.net> <55A8EABE.1060308@huawei.com> <20150717115505.GF19282@twins.programming.kicks-ass.net> <20150717115615.GA18673@twins.programming.kicks-ass.net> <55A8EE83.3000708@huawei.com> <20150717121836.GH19282@twins.programming.kicks-ass.net> In-Reply-To: <20150717121836.GH19282@twins.programming.kicks-ass.net> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.111.66.109] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1957 Lines: 53 On 2015/7/17 20:18, Peter Zijlstra wrote: > On Fri, Jul 17, 2015 at 08:01:07PM +0800, Wangnan (F) wrote: >> >> On 2015/7/17 19:56, Peter Zijlstra wrote: >>> On Fri, Jul 17, 2015 at 01:55:05PM +0200, Peter Zijlstra wrote: >>>> On Fri, Jul 17, 2015 at 07:45:02PM +0800, Wangnan (F) wrote: >>>> >>>>>> Depends on what all you need, if you need full perf events to work then >>>>>> yes perf_event_read_value() is your only option. >>>>>> >>>>>> But note that that requires scheduling, so you cannot actually use it >>>>>> for tracing purposes etc.. >>>>> What you mean "full perf events"? Even with your code some event still not >>>>> work? >>>> The code I posted only works for events that do not have inherit set. >>>> And only works from IRQ/NMI context for events that monitor the current >>>> task or the current CPU (although that needs a little extra code still). >>>> >>>> Anything else and it does not work (correctly). >>> Scratch that from NMI, for that to work we need more magic still. >> The scheduling you said is caused by >> >> mutex_lock(&event->child_mutex) >> >> right? >> >> What about replacing it to mutex_trylock() and simply return an error >> if it read from a BPF program? > That is vile and unreliable. > > I think you really want to put very strict limits on what kind of events > you accept, or create the events yourself. > I think we can check the limitation in BPF program. What about this: event must on current CPU or must be on current process. If not, bpf_read_pmu() should simply return an error. With current design it is easy to implement, and users can still control it through bpf map. But what if we really want cross-cpu PMU accessing? Impossible? Thank you. -- 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/