From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757118AbbJVJtG (ORCPT ); Thu, 22 Oct 2015 05:49:06 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:48191 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756988AbbJVJtC (ORCPT ); Thu, 22 Oct 2015 05:49:02 -0400 Date: Thu, 22 Oct 2015 11:49:02 +0200 From: Peter Zijlstra To: "Wangnan (F)" Cc: 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, pi3orama@163.com, hekuang@huawei.com, netdev@vger.kernel.org Subject: Re: [PATCH V5 1/1] bpf: control events stored in PERF_EVENT_ARRAY maps trace data output when perf sampling Message-ID: <20151022094902.GM2508@worktop.programming.kicks-ass.net> References: <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> <5628423B.4010504@huawei.com> <5628535F.5060505@plumgrid.com> <56285410.3060505@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <56285410.3060505@huawei.com> User-Agent: Mutt/1.5.22.1 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 22, 2015 at 11:12:16AM +0800, Wangnan (F) wrote: > On 2015/10/22 11:09, Alexei Starovoitov wrote: > >On 10/21/15 6:56 PM, Wangnan (F) wrote: > >>>One alternative solution I can image is to attach a BPF program > >>>at sampling like kprobe, and return 0 if we don't want sampling > >>>take action. Thought? > >> > >>Do you think attaching BPF programs to sampling is an acceptable idea? > > > >If you mean to extend 'filter' concept to sampling events? > >So instead of soft_disable of non-local events, you'll attach bpf > >program to sampling events and use map lookup to decide whether > >to filter out or not such sampling event? > > Yes. One could overload or stack the overflow handler I suppose. But this would be in line with the software/tracepoint events calling eBPF muck on trigger, right? > >What pt_regs would be in such case? > Sampling is based on interruption. We can use pt_reg captured by the IRQ > handler, s/IRQ/NMI/ Also, we 'edit' the pt_regs on the way down to the overflow handler as sometimes 'better' information can be had from PMU state. But a pt_regs is available there.