From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Wu, Feng" Subject: Re: Requesting for freeze exception for VT-d posted-interrupts Date: Tue, 14 Jul 2015 05:51:02 +0000 Message-ID: References: <20150713110041.GD4108@zion.uk.xensource.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20150713110041.GD4108@zion.uk.xensource.com> Content-Language: en-US List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Wei Liu Cc: "Tian, Kevin" , "Wu, Feng" , George Dunlap , "andrew.cooper3@citrix.com" , "Wang, Yong Y" , "xen-devel@lists.xen.org" , "Jan Beulich (JBeulich@suse.com)" , "Zhang, Yang Z" List-Id: xen-devel@lists.xenproject.org > -----Original Message----- > From: Wei Liu [mailto:wei.liu2@citrix.com] > Sent: Monday, July 13, 2015 7:01 PM > To: Wu, Feng > Cc: wei.liu2@citrix.com; xen-devel@lists.xen.org; Jan Beulich > (JBeulich@suse.com); andrew.cooper3@citrix.com; George Dunlap; Tian, Kevin; > Zhang, Yang Z; Wang, Yong Y > Subject: Re: Requesting for freeze exception for VT-d posted-interrupts > > On Mon, Jul 13, 2015 at 06:55:30AM +0000, Wu, Feng wrote: > > Hi maintainers, > > > > We would like to request an extension for freeze exception for VT-d > posted-interrupts patch-set. > > > > 1. clarify the state of patch series / feature. > > [v3 01/15] Vt-d Posted-interrupt (PI) design > > Reviewed-by: Kevin Tian > > > > [v3 02/15] Add helper macro for X86_FEATURE_CX16 feature detection > > Reviewed-by: Kevin Tian > > Reviewed-by: Andrew Cooper > > > > [v3 04/15] iommu: Add iommu_intpost to control VT-d Posted-Interrupts > feature > > Reviewed-by: Kevin Tian > > > > [v3 06/15] vmx: Extend struct pi_desc to support VT-d Posted-Interrupts > > Reviewed-by: Andrew Cooper > > Acked-by: Kevin Tian > > > > [v3 07/15] vmx: Initialize VT-d Posted-Interrupts Descriptor > > Acked-by: Kevin Tian > > > > [v3 09/15] vt-d: Extend struct iremap_entry to support VT-d > Posted-Interrupts > > Acked-by: Kevin Tian > > > > [v3 10/15] vt-d: Add API to update IRTE when VT-d PI is used > > Acked-by: Kevin Tian > > > > [v3 13/15] vmx: Properly handle notification event when vCPU is running > > Acked-by: Kevin Tian > > > > [v3 14/15] Update Posted-Interrupts Descriptor during vCPU scheduling > > Acked-by: Kevin Tian > > > > [v3 15/15] Add a command line parameter for VT-d posted-interrupts > > Reviewed-by: Kevin Tian > > > > 2. explain why it needs to be in this release (benefits). > > VT-d posted-interrupts is an important interrupt virtualization feature for > > device pass-through, the running guest can handle external interrupts > > in non-root mode, hence it can eliminate the VM-Exits caused by external > > interrupts. Please refer to the design doc: > > http://lists.xenproject.org/archives/html/xen-devel/2015-06/msg03691.html > > > > >From our experimental environment, after using VT-d posted-interrupts, we > > measured 25% improvement in transaction rate netperf TCP_RR benchmark > > and 28% reduction in host CPU utilization when using assigned devices. > > (10G NIC in my test). > > > > 3. explain why it doesn't break things (risks). > > This feature only exists in Broadwell Server platform, it has no effect on the > > current hardware. > > > > You miss the part that how much common code it touches. There is still > risk of breaking VMX and VT-D even if PI is disabled. > > > 4. CC relevant maintainers and release manager. > > Done > > > > There are two main outstanding issues so far: > > 1. Jan's security concern. I have proposed some solutions but Jan still has > > some problems with my proposals. It would be great if Jan can give a clear > > proposal so that we can discuss and keep making progress. > > 2. Scheduler issue: there are conflicts among maintainers Jan/George/Dario. > > I would agree with Jan's suggestion below: > > > > " Doing this in a central place is certainly the right approach, but > > adding an arch hook that needs to be called everywhere > > vcpu_runstate_change() wouldn't serve that purpose. Instead > > we'd need to replace all current vcpu_runstate_change() calls > > with calls to a new function calling both this and the to be added > > arch hook." > > > > Given the current time scale now, I think it would be very hard to get > these two concerns addressed within a week. Xen has always taken > security serious, I don't want to rush in a feature with possible flawed > design. > > My answer to this request is no until these concerns are addressed. Is it possible to get to 4.6 if making this feature default off? Thanks, Feng > > > However, if different maintainers still hold different opinions, I would > appreciate > > it if maintainers can reach consensus among themselves so that we can keep > > making progress > > > > Yes, this is fore sure. This is what we need to do to work as a > community whether this feature is aimed for 4.6 or not. > > Wei. > > > Thanks, > > Feng