From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Tue, 29 Jul 2014 19:34:38 +0200 (CEST) Received: from mx1.redhat.com ([209.132.183.28]:23630 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by eddie.linux-mips.org with ESMTP id S6859956AbaG2RdeWzI1s (ORCPT ); Tue, 29 Jul 2014 19:33:34 +0200 Received: from int-mx13.intmail.prod.int.phx2.redhat.com (int-mx13.intmail.prod.int.phx2.redhat.com [10.5.11.26]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id s6THXIsh012100 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 29 Jul 2014 13:33:18 -0400 Received: from tranklukator.brq.redhat.com (dhcp-1-191.brq.redhat.com [10.34.1.191]) by int-mx13.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with SMTP id s6THXFaH025506; Tue, 29 Jul 2014 13:33:15 -0400 Received: by tranklukator.brq.redhat.com (nbSMTP-1.00) for uid 500 oleg@redhat.com; Tue, 29 Jul 2014 19:31:39 +0200 (CEST) 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) X-Scanned-By: MIMEDefang 2.68 on 10.5.11.26 Return-Path: X-Envelope-To: <"|/home/ecartis/ecartis -s linux-mips"> (uid 0) X-Orcpt: rfc822;linux-mips@linux-mips.org Original-Recipient: rfc822;linux-mips@linux-mips.org X-archive-position: 41792 X-ecartis-version: Ecartis v1.0.0 Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org X-original-sender: oleg@redhat.com Precedence: bulk List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-Id: linux-mips X-List-ID: linux-mips List-subscribe: List-owner: List-post: List-archive: X-list: linux-mips 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. From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx1.redhat.com ([209.132.183.28]:23630 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by eddie.linux-mips.org with ESMTP id S6859956AbaG2RdeWzI1s (ORCPT ); Tue, 29 Jul 2014 19:33:34 +0200 Date: Tue, 29 Jul 2014 19:31:36 +0200 From: Oleg Nesterov 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: Return-Path: Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-subscribe: List-owner: List-post: List-archive: 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" Message-ID: <20140729173136.y2hECKelI73nJs3srYq8f56wp_qEX_l5_pj-vIQYppo@z> 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.