From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeremy Fitzhardinge Subject: Re: [PATCH 2/10] x86: convert to generic helpers for IPI function calls Date: Wed, 30 Apr 2008 07:51:50 -0700 Message-ID: <48188786.7020609@goop.org> References: <1209453990-7735-1-git-send-email-jens.axboe@oracle.com> <1209453990-7735-3-git-send-email-jens.axboe@oracle.com> <481786A5.7010604@goop.org> <20080430113542.GZ12774@kernel.dk> <20080430122001.GS11126@linux.vnet.ibm.com> <20080430123136.GB12774@kernel.dk> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20080430123136.GB12774-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org> Sender: linux-arch-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: To: Jens Axboe Cc: "Paul E. McKenney" , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org, npiggin-l3A5Bk7waGM@public.gmane.org, linux-arch-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, mingo-X9Un+BFzKDI@public.gmane.org Jens Axboe wrote: > Xen could just stuff that bit into its arch_send_call_function_ipi(), > something like the below should be fine. My question to Jeremy was more > of the order of whether it should be kept or not, I guess it's safer to > just keep it and retain the existing behaviour (and let Jeremy/others > evaluate it at will later on). Note that I got rid of the yield bool and > break when we called the hypervisor. > Yes, it's a nice cleanup. > Jeremy, shall I add this? > Hold off for now. Given that its effects are unmeasured, I'm not even sure its the right thing to do. For example, it will yield if you're sending an IPI to a vcpu which wants to run but can't, but does nothing for an idle vcpu. And always yielding may be a performance problem if the IPI doesn't involve any cpu contention. It's easy to add back if it turns out to be useful. J From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gw.goop.org ([64.81.55.164]:43832 "EHLO mail.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758743AbYD3OwF (ORCPT ); Wed, 30 Apr 2008 10:52:05 -0400 Message-ID: <48188786.7020609@goop.org> Date: Wed, 30 Apr 2008 07:51:50 -0700 From: Jeremy Fitzhardinge MIME-Version: 1.0 Subject: Re: [PATCH 2/10] x86: convert to generic helpers for IPI function calls References: <1209453990-7735-1-git-send-email-jens.axboe@oracle.com> <1209453990-7735-3-git-send-email-jens.axboe@oracle.com> <481786A5.7010604@goop.org> <20080430113542.GZ12774@kernel.dk> <20080430122001.GS11126@linux.vnet.ibm.com> <20080430123136.GB12774@kernel.dk> In-Reply-To: <20080430123136.GB12774@kernel.dk> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-arch-owner@vger.kernel.org List-ID: To: Jens Axboe Cc: "Paul E. McKenney" , linux-kernel@vger.kernel.org, peterz@infradead.org, npiggin@suse.de, linux-arch@vger.kernel.org, mingo@elte.hu Message-ID: <20080430145150.Rzqm68NjX9S-Mem48oUHe1wL-DacRS35co8Fjip96kA@z> Jens Axboe wrote: > Xen could just stuff that bit into its arch_send_call_function_ipi(), > something like the below should be fine. My question to Jeremy was more > of the order of whether it should be kept or not, I guess it's safer to > just keep it and retain the existing behaviour (and let Jeremy/others > evaluate it at will later on). Note that I got rid of the yield bool and > break when we called the hypervisor. > Yes, it's a nice cleanup. > Jeremy, shall I add this? > Hold off for now. Given that its effects are unmeasured, I'm not even sure its the right thing to do. For example, it will yield if you're sending an IPI to a vcpu which wants to run but can't, but does nothing for an idle vcpu. And always yielding may be a performance problem if the IPI doesn't involve any cpu contention. It's easy to add back if it turns out to be useful. J