From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) by ozlabs.org (Postfix) with ESMTP id DDDE6B6EF3 for ; Sun, 27 Jun 2010 17:53:07 +1000 (EST) Message-ID: <4C27035D.1010604@redhat.com> Date: Sun, 27 Jun 2010 10:53:01 +0300 From: Avi Kivity MIME-Version: 1.0 To: Benjamin Herrenschmidt Subject: Re: [PATCH 1/2] KVM: PPC: Add generic hpte management functions References: <1277127841-32704-1-git-send-email-agraf@suse.de> <4C20A64D.2070805@redhat.com> <4C20A6C8.4070002@suse.de> <4C20A795.6040607@redhat.com> <4C20A836.2010908@suse.de> <4C20A890.9040806@redhat.com> <4C20A91A.1080607@suse.de> <4C20AA9B.8000807@redhat.com> <1277593118.4200.122.camel@pasglop> In-Reply-To: <1277593118.4200.122.camel@pasglop> Content-Type: text/plain; charset=UTF-8; format=flowed Cc: kvm-ppc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, Alexander Graf , kvm@vger.kernel.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On 06/27/2010 01:58 AM, Benjamin Herrenschmidt wrote: > >> Then mmu intensive loads can expect to be slow. >> > Well, depends. ppc64 indeed requires the hash to be managed by the > hypervisor, so inserting or invalidating translations will mean a > roundtrip to the hypervisor, though there are ways at least the > insertion could be alleviated (for example, the HV could service the > hash misses directly walking the guest page tables). > But the guest page tables are software defined, no? That means the interface will break if the page table format changes. > But that's due in part to a design choice (whether it's a good one or > not I'm not going to argue here) which favors huge reasonably static > workloads where the hash is expected to contain all translations for > everything. > What about when you have memory pressure? The hash will have to reflect those pte_clear_flush_young(), no? It seems horribly expensive. > However, note that BookE (the embedded variant of the architecture) uses > a different model for virtualization, including options in its latest > variant for a HW logical->real translation (via a small dedicated TLB) > and direct access to some TLB ops from the guest. > I'm somewhat familiar with it, yes. -- error compiling committee.c: too many arguments to function