From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl0-f71.google.com (mail-pl0-f71.google.com [209.85.160.71]) by kanga.kvack.org (Postfix) with ESMTP id C98786B0003 for ; Thu, 5 Apr 2018 11:47:33 -0400 (EDT) Received: by mail-pl0-f71.google.com with SMTP id y7-v6so5644160plh.7 for ; Thu, 05 Apr 2018 08:47:33 -0700 (PDT) Received: from mga01.intel.com (mga01.intel.com. [192.55.52.88]) by mx.google.com with ESMTPS id bj11-v6si6374704plb.525.2018.04.05.08.47.32 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 05 Apr 2018 08:47:32 -0700 (PDT) From: "Wang, Wei W" Subject: RE: [PATCH v30 2/4] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT Date: Thu, 5 Apr 2018 15:47:28 +0000 Message-ID: <286AC319A985734F985F78AFA26841F7394A889E@shsmsx102.ccr.corp.intel.com> References: <1522771805-78927-1-git-send-email-wei.w.wang@intel.com> <1522771805-78927-3-git-send-email-wei.w.wang@intel.com> <20180403214147-mutt-send-email-mst@kernel.org> <5AC43377.2070607@intel.com> <20180404155907-mutt-send-email-mst@kernel.org> <286AC319A985734F985F78AFA26841F7394A6E96@shsmsx102.ccr.corp.intel.com> <20180405040900-mutt-send-email-mst@kernel.org> <286AC319A985734F985F78AFA26841F7394A7F3B@shsmsx102.ccr.corp.intel.com> <20180405170248-mutt-send-email-mst@kernel.org> In-Reply-To: <20180405170248-mutt-send-email-mst@kernel.org> Content-Language: en-US Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Sender: owner-linux-mm@kvack.org List-ID: To: "Michael S. Tsirkin" Cc: "virtio-dev@lists.oasis-open.org" , "linux-kernel@vger.kernel.org" , "virtualization@lists.linux-foundation.org" , "kvm@vger.kernel.org" , "linux-mm@kvack.org" , "mhocko@kernel.org" , "akpm@linux-foundation.org" , "pbonzini@redhat.com" , "liliang.opensource@gmail.com" , "yang.zhang.wz@gmail.com" , "quan.xu0@gmail.com" , "nilal@redhat.com" , "riel@redhat.com" , "huangzhichao@huawei.com" On Thursday, April 5, 2018 10:04 PM, Michael S. Tsirkin wrote: > On Thu, Apr 05, 2018 at 02:05:03AM +0000, Wang, Wei W wrote: > > On Thursday, April 5, 2018 9:12 AM, Michael S. Tsirkin wrote: > > > On Thu, Apr 05, 2018 at 12:30:27AM +0000, Wang, Wei W wrote: > > > > On Wednesday, April 4, 2018 10:08 PM, Michael S. Tsirkin wrote: > > > > > On Wed, Apr 04, 2018 at 10:07:51AM +0800, Wei Wang wrote: > > > > > > On 04/04/2018 02:47 AM, Michael S. Tsirkin wrote: > > > > > > > On Wed, Apr 04, 2018 at 12:10:03AM +0800, Wei Wang wrote: > > > > I'm afraid the driver couldn't be aware if the added hints are > > > > stale or not, > > > > > > > > > No - I mean that driver has code that compares two values and stops > > > reporting. Can one of the values be stale? > > > > The driver compares "vb->cmd_id_use !=3D vb->cmd_id_received" to decide > > if it needs to stop reporting hints, and cmd_id_received is what the > > driver reads from host (host notifies the driver to read for the > > latest value). If host sends a new cmd id, it will notify the guest to > > read again. I'm not sure how that could be a stale cmd id (or maybe I > > misunderstood your point here?) > > > > Best, > > Wei >=20 > The comparison is done in one thread, the update in another one. I think this isn't something that could be solved by adding a lock, unless = host waits for the driver's ACK about finishing the update (this is not agr= eed in the QEMU part discussion). Actually virtio_balloon has F_IOMMU_PLATFORM disabled, maybe we don't need = to worry about that using DMA api case (we only have gpa added to the vq, a= nd having some entries stay in the vq seems fine). For this feature, I thin= k it would not work with F_IOMMU enabled either. If there is any further need (I couldn't think of a need so far), I think w= e could consider to let host inject a vq interrupt at some point, and then = the driver handler can do the virtqueue_get_buf work. Best, Wei