Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932085AbaJVI0f (ORCPT ); Wed, 22 Oct 2014 04:26:35 -0400 Received: from e06smtp12.uk.ibm.com ([195.75.94.108]:58480 "EHLO e06smtp12.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750813AbaJVI0d (ORCPT ); Wed, 22 Oct 2014 04:26:33 -0400 Date: Wed, 22 Oct 2014 10:26:25 +0200 From: Heiko Carstens To: Vojtech Pavlik Cc: Ananth N Mavinakayanahalli , Anil S Keshavamurthy , "David S. Miller" , Masami Hiramatsu , Ingo Molnar , Jiri Kosina , Jiri Slaby , Steven Rostedt , Martin Schwidefsky , linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 0/2] s390 vs. kprobes on ftrace Message-ID: <20141022082625.GB4090@osiris> References: <1413880229-4796-1-git-send-email-heiko.carstens@de.ibm.com> <20141021195831.GA31587@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141021195831.GA31587@suse.cz> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14102208-0009-0000-0000-000001A27F00 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 21, 2014 at 09:58:31PM +0200, Vojtech Pavlik wrote: > Hello Heiko, > > I can confirm that kGraft works well on top of current mainline with > this patch added. > > Another reason for a performance impact when kGraft is enabled is that > kGraft still adds two instructions to the syscall path on s390x, as > there is no space left for a kgraft TIF in the first eight bits of > thread info flags. Renumbering the thread info flags such that _TIF_WORK > occupies the first eight bits and TIF_TRACE the next eight would fix > that problem: Do you believe it is feasible? Hi Vojtech, I think you're talking about the SLES12 kernel? There you can simply move the TIF_SYSCALL bit to the same byte where your TIF_KGR bit resides. Upstream is a bit different since the TIF_SYSCALL bit is already gone (got replaced with an s390 specific "PIF" bit). However the free TIF bit got already eaten up by uprobes.. However we can think of a better solution for upstream if the combined solution of kGraft/kpatch is ready to be merged. -- 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/