From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753784AbbJUODV (ORCPT ); Wed, 21 Oct 2015 10:03:21 -0400 Received: from m12-13.163.com ([220.181.12.13]:38437 "EHLO m12-13.163.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751292AbbJUODT convert rfc822-to-8bit (ORCPT ); Wed, 21 Oct 2015 10:03:19 -0400 Content-Type: text/plain; charset=gb2312 Mime-Version: 1.0 (1.0) Subject: Re: [PATCH V5 1/1] bpf: control events stored in PERF_EVENT_ARRAY maps trace data output when perf sampling From: pi3orama X-Mailer: iPhone Mail (13A452) In-Reply-To: <20151021134951.GH3604@twins.programming.kicks-ass.net> Date: Wed, 21 Oct 2015 22:01:46 +0800 Cc: "Wangnan (F)" , Alexei Starovoitov , xiakaixu , davem@davemloft.net, acme@kernel.org, mingo@redhat.com, masami.hiramatsu.pt@hitachi.com, jolsa@kernel.org, daniel@iogearbox.net, linux-kernel@vger.kernel.org, hekuang@huawei.com, netdev@vger.kernel.org Content-Transfer-Encoding: 8BIT Message-Id: <1D2C9396-01CB-4981-B493-EA311F0457E7@163.com> References: <1445325735-121694-1-git-send-email-xiakaixu@huawei.com> <1445325735-121694-2-git-send-email-xiakaixu@huawei.com> <5626C5CE.8080809@plumgrid.com> <20151021091254.GF2881@worktop.programming.kicks-ass.net> <56276968.6070604@huawei.com> <20151021113316.GM17308@twins.programming.kicks-ass.net> <56277BCE.6030400@huawei.com> <20151021121713.GC3604@twins.programming.kicks-ass.net> <56279634.5000606@huawei.com> <20151021134951.GH3604@twins.programming.kicks-ass.net> To: Peter Zijlstra X-CM-TRANSID: DcCowAA3l1TLmidWId+ZAA--.14074S2 X-Coremail-Antispam: 1Uf129KBjvdXoWrZw4DCFWDKr1UtF43CFyDWrg_yoWxtrgEgw 1xZwn7uw1UJFn3tasF9rW7AFsFqw4rKa4UJrs5GwsrKas5ZF40kFnYyFyrt342yr40qrs0 grnxAr1UZr93ujkaLaAFLSUrUUUUUb8apTn2vfkv8UJUUUU8Yxn0WfASr-VFAUDa7-sFnT 9fnUUvcSsGvfC2KfnxnUUI43ZEXa7IU8bTmDUUUUU== X-Originating-IP: [223.104.3.194] X-CM-SenderInfo: lslt02xdpdqiywtou0bp/1tbiXwGaQFWBPJlMOAADsC Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 发自我的 iPhone > 在 2015年10月21日，下午9:49，Peter Zijlstra 写道： > >> On Wed, Oct 21, 2015 at 09:42:12PM +0800, Wangnan (F) wrote: >> How can an eBPF program access a !local event: >> >> when creating perf event array we don't care which perf event >> is for which CPU, so perf program can access any perf event in >> that array. > > So what is stopping the eBPF thing from calling perf_event_read_local() > on a !local event and triggering a kernel splat? I can understand the perf_event_read_local() case, but I really can't understand what is stopping us to write to an atomic field belong to a !local perf event. Could you please give a further explanation? Thank you. >