Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751660AbaG2ReI (ORCPT ); Tue, 29 Jul 2014 13:34:08 -0400 Received: from mx1.redhat.com ([209.132.183.28]:62559 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751417AbaG2ReG (ORCPT ); Tue, 29 Jul 2014 13:34:06 -0400 Date: Tue, 29 Jul 2014 19:31:36 +0200 From: Oleg Nesterov To: Andy Lutomirski Cc: "linux-kernel@vger.kernel.org" , Kees Cook , Will Drewry , X86 ML , "linux-arm-kernel@lists.infradead.org" , Linux MIPS Mailing List , linux-arch , LSM List , Alexei Starovoitov , "H. Peter Anvin" Subject: Re: [PATCH v3 6/8] x86: Split syscall_trace_enter into two phases Message-ID: <20140729173136.GA2808@redhat.com> References: <3f649f5658a163645e3ce15156176c325283762e.1405992946.git.luto@amacapital.net> <20140728173723.GA20993@redhat.com> <20140729165416.GA967@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 On 07/29, Andy Lutomirski wrote: > > On Tue, Jul 29, 2014 at 9:54 AM, Oleg Nesterov wrote: > > > > Yes, just to trigger the slow path, I guess. > > > >> I'll update the code to call user_exit iff TIF_NOHZ is > >> set. > > > > Or perhaps it would be better to not add another user of this (strange) flag > > and just call user_exit() unconditionally(). But, yes, you need to use > > from "work = flags & (_TIF_WORK_SYSCALL_ENTRY & ~TIF_NOHZ)" then.\ > > user_exit looks slow enough to me that a branch to try to avoid it may > be worthwhile. I bet that explicitly checking the flag is > actually both faster and clearer. I don't think so (unless I am confused again), note that user_exit() uses jump label. But this doesn't matter. I meant that we should avoid TIF_NOHZ if possible because I think it should die somehow (currently I do not know how ;). And because it is ugly to check the same condition twice: if (work & TIF_NOHZ) { // user_exit() if (context_tracking_is_enabled()) context_tracking_user_exit(); } TIF_NOHZ is set if and only if context_tracking_is_enabled() is true. So I think that work = current_thread_info()->flags & (_TIF_WORK_SYSCALL_ENTRY & ~TIF_NOHZ); user_exit(); looks a bit better. But I won't argue. > That's what I did for v4. I am going to read it today. Not that I think I can help or find something wrong. 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/