Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752186Ab2KFST5 (ORCPT ); Tue, 6 Nov 2012 13:19:57 -0500 Received: from mx1.redhat.com ([209.132.183.28]:46372 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751571Ab2KFST4 (ORCPT ); Tue, 6 Nov 2012 13:19:56 -0500 Date: Tue, 6 Nov 2012 19:20:00 +0100 From: Oleg Nesterov To: Josh Stone Cc: Srikar Dronamraju , Ananth N Mavinakayanahalli , Anton Arapov , David Smith , "Frank Ch. Eigler" , Ingo Molnar , Peter Zijlstra , "Suzuki K. Poulose" , linux-kernel@vger.kernel.org Subject: Re: uprobes && pre-filtering Message-ID: <20121106182000.GA3522@redhat.com> References: <20121105190446.GA6188@redhat.com> <20121106090525.GB27055@linux.vnet.ibm.com> <20121106170243.GA32311@redhat.com> <50994BC1.1000705@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <50994BC1.1000705@redhat.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2893 Lines: 79 On 11/06, Josh Stone wrote: > > On 11/06/2012 09:02 AM, Oleg Nesterov wrote: > >>> - Perhaps we should extend the API. We can add > >>> > >>> uprobe_apply(consumer, task, bool add_remove); > >>> > >>> which adds/removes breakpoints to task->mm. > >>> > >>> This way consumer can probe every task it wants to trace after > >>> uprobe_register(). > >>> > >>> Its ->filter(UPROBE_FILTER_REGISTER) should simply return false. Or, > >>> better, we can split uprobe_register() into 2 functions, > >>> __uprobe_register() and uprobe_apply_all() which actually does > >>> register_for_each_vma(). > >>> > >>> ***** QUESTION *****: perhaps this is all systemtap needs? ignoring > >>> UPROBE_FILTER_MMAP. > >>> > >> So in this case, would uprobe_register() just add a consumer to a > >> new/existing uprobe. The actual probe insertion is done by the > >> uprobe_apply()/uprobe_apply_all(). > > > > Yes. Not sure we really need this, but to me this extension looks natural. > > > > Frank, Josh, do you think it can help systemtap ? > > Yes, I think this sounds closer to systemtap's model of probing. We > already track tasks that come and go to see which are "interesting", so > we could easily call apply() at that time. We actually watch mmaps too, > so I think we could apply() for that case as well. OK, thanks. (just in case, mmap is different, but lets ignore this now). > We wouldn't even need filtering functions at all in this mode. But > maybe other consumers could still use it, like perf. Of course, we need ->filter() anyway. > However, it's not clear to me what value there is in uprobe_register, if > you always have to apply it too. The modes are something like: > > 1. uprobe_register(); uprobe_apply_all(); > 2. uprobe_register(); uprobe_apply(); [...] No, no, sorry for confusion. I meant we could add __uprobe_register() (or whatever) which doesn't actually insert the breakpoint. So if the tracer relies on uprobe_apply() it can avoid the costly register_for_each_vma/filter and do __uprobe_register + apply. This is not strictly necessary even if we add uprobe_apply*, and you can always use uprobe_register() (or uprobe_register_all as you denoted it below). > first applicable task to come around. So why not instead: > > 1. uprobe_register_all(); > 2. uprobe_register_task(); [...] > > In this case, the second would have to allow the same consumer to be > repeated on different tasks, but it feels more natural to me. This can work too. But uprobe_unregister_task() doesn't look very clear. What should it do? IOW, you still need uprobe_unregister_all() and this doesn't look symmetrical. Oleg. -- 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/