Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756089AbZCNDst (ORCPT ); Fri, 13 Mar 2009 23:48:49 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752326AbZCNDsl (ORCPT ); Fri, 13 Mar 2009 23:48:41 -0400 Received: from gate.crashing.org ([63.228.1.57]:43208 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752055AbZCNDsk (ORCPT ); Fri, 13 Mar 2009 23:48:40 -0400 Subject: Re: [patch 02/11] x86 architecture implementation of Hardware Breakpoint interfaces From: Benjamin Herrenschmidt To: prasad@linux.vnet.ibm.com Cc: Alan Stern , Ingo Molnar , Andrew Morton , Linux Kernel Mailing List , Roland McGrath In-Reply-To: <20090311174115.GD9547@in.ibm.com> References: <20090311121220.GI2282@elte.hu> <20090311174115.GD9547@in.ibm.com> Content-Type: text/plain Date: Sat, 14 Mar 2009 14:47:35 +1100 Message-Id: <1237002455.25062.83.camel@pasglop> Mime-Version: 1.0 X-Mailer: Evolution 2.24.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1229 Lines: 28 On Wed, 2009-03-11 at 23:11 +0530, K.Prasad wrote: > With FCFS or an allocation mechanism without the (un)installed() > callbacks we'd lose the ability to record requests and service them > later when registers become availabile. > > Say when (un)installed() callbacks are implemented for the proposed > ftrace-plugin to trace kernel symbols, they can automatically stop/start > tracing as and when registers become (un)available. This can be helpful when > we wish to profile memory access over a kernel variable for a long duration > (where small loss of tracing data can be tolerated), while the system would > permit simultaneous user-space access (say a GDB session using 'hbreak'). > > Are we fine with disallowing such usage, which if done will let the requester > of the breakpoint register 'poll' periodically to check availability. Is that such a big deal ? Can't we just have the kernel degrade to classic SW breakpoints ? Smells like overengineering to me ... Ben. -- 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/