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(p200300cbc707a1000e2041dac49b8974.dip0.t-ipconnect.de. [2003:cb:c707:a100:e20:41da:c49b:8974]) by smtp.gmail.com with ESMTPSA id z1-20020adff1c1000000b002c70c99db74sm12379651wro.86.2023.03.07.03.24.13 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 07 Mar 2023 03:24:14 -0800 (PST) Message-ID: <9159ed0c-4d09-a633-813c-11b8c72fbf9b@redhat.com> Date: Tue, 7 Mar 2023 12:24:13 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.8.0 Subject: Re: [PATCH v1 2/2] vhost: Remove vhost_backend_can_merge() callback Content-Language: en-US To: Igor Mammedov Cc: qemu-devel@nongnu.org, "Michael S. Tsirkin" , Stefan Hajnoczi , "Dr . David Alan Gilbert" References: <20230216114752.198627-1-david@redhat.com> <20230216114752.198627-3-david@redhat.com> <20230307112548.062b068d@imammedo.users.ipa.redhat.com> <20230307121644.755438a3@imammedo.users.ipa.redhat.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20230307121644.755438a3@imammedo.users.ipa.redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=david@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 07.03.23 12:16, Igor Mammedov wrote: > On Tue, 7 Mar 2023 11:25:48 +0100 > Igor Mammedov wrote: > >> On Thu, 16 Feb 2023 12:47:52 +0100 >> David Hildenbrand wrote: >> >>> Checking whether the memory regions are equal is sufficient: if they are >>> equal, then most certainly the contained fd is equal. >> sounds reasonable to me. >> >>> >>> The whole vhost-user memslot handling is suboptimal and overly >>> complicated. We shouldn't have to lookup a RAM memory regions we got >>> notified about in vhost_user_get_mr_data() using a host pointer. But that >> >> While on janitor duty can you fixup following? >> >> vhost_user_get_mr_data() -> memory_region_from_host -> >> -> qemu_ram_block_from_host() >> for qemu_ram_block_from_host doc comment seems to out of >> sync (ram_addr not longer exists) >> >>> requires a bigger rework -- especially an alternative vhost_set_mem_table() >>> backend call that simply consumes MemoryRegionSections. >> >> just skimming through usage of vhost_user_get_mr_data() it looks like >> we are first collecting MemoryRegionSection-s into tmp_sections >> then we do vhost_commit we convert then into vhost_memory_region list >> and the we are trying hard to convert addresses from the later >> to back to MemoryRegions we've lost during tmp_sections conversion >> all over the place. >> >> To me it looks like we should drop conversion to vhost_dev::mem >> and replace its usage with vhost_dev::mem_sections directly >> to get rid of data duplication and back and forth addr<->mr conversion. >> >>> For now, let's just drop vhost_backend_can_merge(). >>> >>> Signed-off-by: David Hildenbrand >> >> Reviewed-by: Igor Mammedov >> >>> --- >>> hw/virtio/vhost-user.c | 14 -------------- >>> hw/virtio/vhost-vdpa.c | 1 - >>> hw/virtio/vhost.c | 6 +----- >>> include/hw/virtio/vhost-backend.h | 4 ---- >>> 4 files changed, 1 insertion(+), 24 deletions(-) >>> >>> diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c >>> index e68daa35d4..4bfaf559a7 100644 >>> --- a/hw/virtio/vhost-user.c >>> +++ b/hw/virtio/vhost-user.c >>> @@ -2195,19 +2195,6 @@ static int vhost_user_migration_done(struct vhost_dev *dev, char* mac_addr) >>> return -ENOTSUP; >>> } >>> >>> -static bool vhost_user_can_merge(struct vhost_dev *dev, >>> - uint64_t start1, uint64_t size1, >>> - uint64_t start2, uint64_t size2) >>> -{ >>> - ram_addr_t offset; >>> - int mfd, rfd; >>> - >>> - (void)vhost_user_get_mr_data(start1, &offset, &mfd); >>> - (void)vhost_user_get_mr_data(start2, &offset, &rfd); >>> - >>> - return mfd == rfd; >>> -} >>> - >>> static int vhost_user_net_set_mtu(struct vhost_dev *dev, uint16_t mtu) >>> { >>> VhostUserMsg msg; >>> @@ -2704,7 +2691,6 @@ const VhostOps user_ops = { >>> .vhost_set_vring_enable = vhost_user_set_vring_enable, >>> .vhost_requires_shm_log = vhost_user_requires_shm_log, >>> .vhost_migration_done = vhost_user_migration_done, >>> - .vhost_backend_can_merge = vhost_user_can_merge, >>> .vhost_net_set_mtu = vhost_user_net_set_mtu, >>> .vhost_set_iotlb_callback = vhost_user_set_iotlb_callback, >>> .vhost_send_device_iotlb_msg = vhost_user_send_device_iotlb_msg, >>> diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c >>> index 542e003101..9ab7bc8718 100644 >>> --- a/hw/virtio/vhost-vdpa.c >>> +++ b/hw/virtio/vhost-vdpa.c >>> @@ -1317,7 +1317,6 @@ const VhostOps vdpa_ops = { >>> .vhost_set_config = vhost_vdpa_set_config, >>> .vhost_requires_shm_log = NULL, >>> .vhost_migration_done = NULL, >>> - .vhost_backend_can_merge = NULL, >>> .vhost_net_set_mtu = NULL, >>> .vhost_set_iotlb_callback = NULL, >>> .vhost_send_device_iotlb_msg = NULL, >>> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c >>> index b7fb960fa9..9d8662aa98 100644 >>> --- a/hw/virtio/vhost.c >>> +++ b/hw/virtio/vhost.c >>> @@ -733,11 +733,7 @@ static void vhost_region_add_section(struct vhost_dev *dev, >>> size_t offset = mrs_gpa - prev_gpa_start; >>> >>> if (prev_host_start + offset == mrs_host && >>> - section->mr == prev_sec->mr && >>> - (!dev->vhost_ops->vhost_backend_can_merge || >>> - dev->vhost_ops->vhost_backend_can_merge(dev, > > another question, can it relly happen, i.e. having 2 abut memory sections > with the same memory region, is yes then when/why? Unfortunately yet, because vhost relies on some hacks (sorry, but that's what it is) to make huge pages work. The following commit contains some details: commit 76525114736e8f669766e69b715fa59ce8648aae Author: Dr. David Alan Gilbert Date: Thu Jan 16 20:24:14 2020 +0000 vhost: Only align sections for vhost-user I added hugepage alignment code in c1ece84e7c9 to deal with vhost-user + postcopy which needs aligned pages when using userfault. However, on x86 the lower 2MB of address space tends to be shotgun'd with small fragments around the 512-640k range - e.g. video RAM, and with HyperV synic pages tend to sit around there - again splitting it up. The alignment code complains with a 'Section rounded to ...' error and gives up. Otherwise it wouldn't be needed, because flatview simplification code already merges what's reasonable. [I'll reply to you pother mail regarding that shortly] -- Thanks, David / dhildenb