From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Thu, 31 Jul 2014 18:49:35 +0200 (CEST) Received: from mail-wg0-f43.google.com ([74.125.82.43]:48340 "EHLO mail-wg0-f43.google.com" rhost-flags-OK-OK-OK-OK) by eddie.linux-mips.org with ESMTP id S6860178AbaGaQt3MT10x (ORCPT ); Thu, 31 Jul 2014 18:49:29 +0200 Received: by mail-wg0-f43.google.com with SMTP id l18so2921100wgh.26 for ; Thu, 31 Jul 2014 09:49:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; bh=biwa6KGHQfrwZUOOlM7kYflPIXtp7/Q6/3kgS2AY2lw=; b=uVY3VOnOv87loC7yenSfNcxYeLuJAXWGhKB3yyN5iR6lDbOmwkFLiHU1FA7EYbdZzU FxLwoA16A6zGYcv37En2dqsfvd5x9kXe3xjGWSBa049HC3e4jBnEybSR+X7jSuQ1BUJ8 ozIgcvVvdYN/ukfPgLwH/B+RTBQAY71KR2IMQ03NCxMcmRevk/HES4SStk24rKB9BCX7 WyuHr4A3sx8eIHoGgti/QYKoqaClV3d61AP76YeTIq6M87hy6hiBWh5H+bL34ersVVmH qcoXL0h6xYCAR7ercye3NUwoYTbB/ZN480xWG6oJ4DLdSKIvlEM4URXceIRCta+8HU/C pfOg== X-Received: by 10.194.189.230 with SMTP id gl6mr18865824wjc.118.1406825363741; Thu, 31 Jul 2014 09:49:23 -0700 (PDT) Received: from localhost (8.20.196.77.rev.sfr.net. [77.196.20.8]) by mx.google.com with ESMTPSA id h3sm14512758wjz.48.2014.07.31.09.49.21 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 31 Jul 2014 09:49:23 -0700 (PDT) Date: Thu, 31 Jul 2014 18:49:20 +0200 From: Frederic Weisbecker To: Oleg Nesterov Cc: Andy Lutomirski , "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 v4 2/5] x86,entry: Only call user_exit if TIF_NOHZ Message-ID: <20140731164918.GC7842@localhost.localdomain> References: <7123b2489cc5d1d5abb7bcf1364ca729cab3e6ca.1406604806.git.luto@amacapital.net> <20140729193232.GA8153@redhat.com> <20140730164344.GA27954@localhost.localdomain> <20140731151630.GA7842@localhost.localdomain> <20140731164246.GA15974@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140731164246.GA15974@redhat.com> User-Agent: Mutt/1.5.23 (2014-03-12) 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: 41844 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: fweisbec@gmail.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 Thu, Jul 31, 2014 at 06:42:46PM +0200, Oleg Nesterov wrote: > On 07/31, Frederic Weisbecker wrote: > > > > On Wed, Jul 30, 2014 at 10:23:34AM -0700, Andy Lutomirski wrote: > > > > > > At the end of the day, the syscall slowpath code calls a bunch of > > > functions depending on what TIF_XYZ flags are set. As long as it's > > > structured like "if (TIF_A) do_a(); if (TIF_B) do_b();" or something > > > like that, it's comprehensible. But once random functions with no > > > explicit flag checks or comments start showing up, it gets confusing. > > > > Yeah that's a point. I don't mind much the TIF_NOHZ test if you like. > > And in my opinion > > if (work & TIF_XYZ) > user_exit(); > > looks even more confusing. Because, once again, TIF_XYZ is not the > reason to call user_exit(). > > Not to mention this adds a minor performance penalty. That's a point too! You guys both convinced me! ;-) > > > > If it's indeed all-or-nothing, I could remove the check and add a > > > comment. But please keep in mind that, currently, the slow path is > > > *slow*, and my patches only improve the entry case. So enabling > > > context tracking on every task will hurt. > > > > That's what we do anyway. I haven't found a safe way to enabled context tracking > > without tracking all CPUs. > > And if we change this, then the code above becomes racy. The state of > TIF_XYZ can be changed right after the check. OK, it is racy anyway ;) > but still this adds more confusion. No because all running tasks have this flag set when context tracking is enabled. And context tracking can't be disabled on runtime. From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wg0-f43.google.com ([74.125.82.43]:48340 "EHLO mail-wg0-f43.google.com" rhost-flags-OK-OK-OK-OK) by eddie.linux-mips.org with ESMTP id S6860178AbaGaQt3MT10x (ORCPT ); Thu, 31 Jul 2014 18:49:29 +0200 Received: by mail-wg0-f43.google.com with SMTP id l18so2921100wgh.26 for ; Thu, 31 Jul 2014 09:49:23 -0700 (PDT) Date: Thu, 31 Jul 2014 18:49:20 +0200 From: Frederic Weisbecker Subject: Re: [PATCH v4 2/5] x86,entry: Only call user_exit if TIF_NOHZ Message-ID: <20140731164918.GC7842@localhost.localdomain> References: <7123b2489cc5d1d5abb7bcf1364ca729cab3e6ca.1406604806.git.luto@amacapital.net> <20140729193232.GA8153@redhat.com> <20140730164344.GA27954@localhost.localdomain> <20140731151630.GA7842@localhost.localdomain> <20140731164246.GA15974@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140731164246.GA15974@redhat.com> 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: Oleg Nesterov Cc: Andy Lutomirski , "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: <20140731164920.osWPyfXNzHPQs7WCbOdqvVu4Gz5--0q18qm5roNI1Ag@z> On Thu, Jul 31, 2014 at 06:42:46PM +0200, Oleg Nesterov wrote: > On 07/31, Frederic Weisbecker wrote: > > > > On Wed, Jul 30, 2014 at 10:23:34AM -0700, Andy Lutomirski wrote: > > > > > > At the end of the day, the syscall slowpath code calls a bunch of > > > functions depending on what TIF_XYZ flags are set. As long as it's > > > structured like "if (TIF_A) do_a(); if (TIF_B) do_b();" or something > > > like that, it's comprehensible. But once random functions with no > > > explicit flag checks or comments start showing up, it gets confusing. > > > > Yeah that's a point. I don't mind much the TIF_NOHZ test if you like. > > And in my opinion > > if (work & TIF_XYZ) > user_exit(); > > looks even more confusing. Because, once again, TIF_XYZ is not the > reason to call user_exit(). > > Not to mention this adds a minor performance penalty. That's a point too! You guys both convinced me! ;-) > > > > If it's indeed all-or-nothing, I could remove the check and add a > > > comment. But please keep in mind that, currently, the slow path is > > > *slow*, and my patches only improve the entry case. So enabling > > > context tracking on every task will hurt. > > > > That's what we do anyway. I haven't found a safe way to enabled context tracking > > without tracking all CPUs. > > And if we change this, then the code above becomes racy. The state of > TIF_XYZ can be changed right after the check. OK, it is racy anyway ;) > but still this adds more confusion. No because all running tasks have this flag set when context tracking is enabled. And context tracking can't be disabled on runtime.