From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754589AbbIHKGC (ORCPT ); Tue, 8 Sep 2015 06:06:02 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:54468 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754157AbbIHKF7 (ORCPT ); Tue, 8 Sep 2015 06:05:59 -0400 Date: Tue, 8 Sep 2015 12:05:51 +0200 From: Peter Zijlstra To: Linus Torvalds Cc: Davidlohr Bueso , Dave Chinner , Linux Kernel Mailing List , Waiman Long , Ingo Molnar Subject: Re: [4.2, Regression] Queued spinlocks cause major XFS performance regression Message-ID: <20150908100551.GC3644@twins.programming.kicks-ass.net> References: <20150904054820.GY3902@dastard> <20150904071143.GZ3902@dastard> <20150904082954.GB3902@dastard> <20150904151427.GG18489@twins.programming.kicks-ass.net> <20150904152523.GR18673@twins.programming.kicks-ass.net> <20150907000546.GA27993@linux-q0g1.site> <20150907065703.GX3644@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Sep 07, 2015 at 01:45:18PM -0700, Linus Torvalds wrote: > On Sun, Sep 6, 2015 at 11:57 PM, Peter Zijlstra wrote: > > > > Just to continue the argument for arguments sake, the function is named > > 'virt' (not paravirt) and tests the HYPERVISOR CPUID bit. How is that > > not appropriately named? > > Well, I think right now one issue is that you can't avoid it, even > when you want pure "raw hardware" spinlocks. The host could choose not to set the HYPERVISOR CPUID bit, but yes point taken, and I've got a patch to make it conditional on a CONFIG thingy. > I really think it should at the very least be inside CONFIG_PARAVIRT. > Because it *is* about helping the hypervisor, so really is about > paravirtualization. Ah, so I think the confusion is in what we consider paravirt to mean. My definition of paravirt is that its a form of virtualization where the guest and host communicate over a software channel. In this case; the guest does not talk to the host, there is no hypercall, no host support required. Therefore this is not paravirt. Wikipedia: https://en.wikipedia.org/wiki/Paravirtualization Seems to agree with such a definition. In any case, no strong feelings either way; the current patch that I've got uses CONFIG_HYPERVISOR_GUEST, but I'm happy to change that to CONFIG_PARAVIRT.