Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751543AbaG2SSj (ORCPT ); Tue, 29 Jul 2014 14:18:39 -0400 Received: from mx1.redhat.com ([209.132.183.28]:16024 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750862AbaG2SSh (ORCPT ); Tue, 29 Jul 2014 14:18:37 -0400 Date: Tue, 29 Jul 2014 20:16:15 +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: <20140729181615.GA4950@redhat.com> References: <3f649f5658a163645e3ce15156176c325283762e.1405992946.git.luto@amacapital.net> <20140728173723.GA20993@redhat.com> <20140729165416.GA967@redhat.com> <20140729173136.GA2808@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 10:31 AM, Oleg Nesterov wrote: > > > > 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. > > I don't get it. Don't worry, you are not alone. > context_tracking_is_enabled is global, and TIF_NOHZ > is per-task. Isn't this stuff determined per-task or per-cpu or > something? > > IOW, if one CPU is running something that's very heavily > userspace-oriented and another CPU is doing something syscall- or > sleep-heavy, then shouldn't only the first CPU end up paying the price > of context tracking? Please see another email I sent to Frederic. 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/