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authorLibravatar Linus Torvalds <torvalds@linux-foundation.org>2023-02-21 18:24:12 -0800
committerLibravatar Linus Torvalds <torvalds@linux-foundation.org>2023-02-21 18:24:12 -0800
commit5b7c4cabbb65f5c469464da6c5f614cbd7f730f2 (patch)
treecc5c2d0a898769fd59549594fedb3ee6f84e59a0 /Documentation/gpu/rfc/i915_vm_bind.rst
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Merge tag 'net-next-6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-nextgrafted
Pull networking updates from Jakub Kicinski: "Core: - Add dedicated kmem_cache for typical/small skb->head, avoid having to access struct page at kfree time, and improve memory use. - Introduce sysctl to set default RPS configuration for new netdevs. - Define Netlink protocol specification format which can be used to describe messages used by each family and auto-generate parsers. Add tools for generating kernel data structures and uAPI headers. - Expose all net/core sysctls inside netns. - Remove 4s sleep in netpoll if carrier is instantly detected on boot. - Add configurable limit of MDB entries per port, and port-vlan. - Continue populating drop reasons throughout the stack. - Retire a handful of legacy Qdiscs and classifiers. Protocols: - Support IPv4 big TCP (TSO frames larger than 64kB). - Add IP_LOCAL_PORT_RANGE socket option, to control local port range on socket by socket basis. - Track and report in procfs number of MPTCP sockets used. - Support mixing IPv4 and IPv6 flows in the in-kernel MPTCP path manager. - IPv6: don't check net.ipv6.route.max_size and rely on garbage collection to free memory (similarly to IPv4). - Support Penultimate Segment Pop (PSP) flavor in SRv6 (RFC8986). - ICMP: add per-rate limit counters. - Add support for user scanning requests in ieee802154. - Remove static WEP support. - Support minimal Wi-Fi 7 Extremely High Throughput (EHT) rate reporting. - WiFi 7 EHT channel puncturing support (client & AP). BPF: - Add a rbtree data structure following the "next-gen data structure" precedent set by recently added linked list, that is, by using kfunc + kptr instead of adding a new BPF map type. - Expose XDP hints via kfuncs with initial support for RX hash and timestamp metadata. - Add BPF_F_NO_TUNNEL_KEY extension to bpf_skb_set_tunnel_key to better support decap on GRE tunnel devices not operating in collect metadata. - Improve x86 JIT's codegen for PROBE_MEM runtime error checks. - Remove the need for trace_printk_lock for bpf_trace_printk and bpf_trace_vprintk helpers. - Extend libbpf's bpf_tracing.h support for tracing arguments of kprobes/uprobes and syscall as a special case. - Significantly reduce the search time for module symbols by livepatch and BPF. - Enable cpumasks to be used as kptrs, which is useful for tracing programs tracking which tasks end up running on which CPUs in different time intervals. - Add support for BPF trampoline on s390x and riscv64. - Add capability to export the XDP features supported by the NIC. - Add __bpf_kfunc tag for marking kernel functions as kfuncs. - Add cgroup.memory=nobpf kernel parameter option to disable BPF memory accounting for container environments. Netfilter: - Remove the CLUSTERIP target. It has been marked as obsolete for years, and we still have WARN splats wrt races of the out-of-band /proc interface installed by this target. - Add 'destroy' commands to nf_tables. They are identical to the existing 'delete' commands, but do not return an error if the referenced object (set, chain, rule...) did not exist. Driver API: - Improve cpumask_local_spread() locality to help NICs set the right IRQ affinity on AMD platforms. - Separate C22 and C45 MDIO bus transactions more clearly. - Introduce new DCB table to control DSCP rewrite on egress. - Support configuration of Physical Layer Collision Avoidance (PLCA) Reconciliation Sublayer (RS) (802.3cg-2019). Modern version of shared medium Ethernet. - Support for MAC Merge layer (IEEE 802.3-2018 clause 99). Allowing preemption of low priority frames by high priority frames. - Add support for controlling MACSec offload using netlink SET. - Rework devlink instance refcounts to allow registration and de-registration under the instance lock. Split the code into multiple files, drop some of the unnecessarily granular locks and factor out common parts of netlink operation handling. - Add TX frame aggregation parameters (for USB drivers). - Add a new attr TCA_EXT_WARN_MSG to report TC (offload) warning messages with notifications for debug. - Allow offloading of UDP NEW connections via act_ct. - Add support for per action HW stats in TC. - Support hardware miss to TC action (continue processing in SW from a specific point in the action chain). - Warn if old Wireless Extension user space interface is used with modern cfg80211/mac80211 drivers. Do not support Wireless Extensions for Wi-Fi 7 devices at all. Everyone should switch to using nl80211 interface instead. - Improve the CAN bit timing configuration. Use extack to return error messages directly to user space, update the SJW handling, including the definition of a new default value that will benefit CAN-FD controllers, by increasing their oscillator tolerance. New hardware / drivers: - Ethernet: - nVidia BlueField-3 support (control traffic driver) - Ethernet support for imx93 SoCs - Motorcomm yt8531 gigabit Ethernet PHY - onsemi NCN26000 10BASE-T1S PHY (with support for PLCA) - Microchip LAN8841 PHY (incl. cable diagnostics and PTP) - Amlogic gxl MDIO mux - WiFi: - RealTek RTL8188EU (rtl8xxxu) - Qualcomm Wi-Fi 7 devices (ath12k) - CAN: - Renesas R-Car V4H Drivers: - Bluetooth: - Set Per Platform Antenna Gain (PPAG) for Intel controllers. - Ethernet NICs: - Intel (1G, igc): - support TSN / Qbv / packet scheduling features of i226 model - Intel (100G, ice): - use GNSS subsystem instead of TTY - multi-buffer XDP support - extend support for GPIO pins to E823 devices - nVidia/Mellanox: - update the shared buffer configuration on PFC commands - implement PTP adjphase function for HW offset control - TC support for Geneve and GRE with VF tunnel offload - more efficient crypto key management method - multi-port eswitch support - Netronome/Corigine: - add DCB IEEE support - support IPsec offloading for NFP3800 - Freescale/NXP (enetc): - support XDP_REDIRECT for XDP non-linear buffers - improve reconfig, avoid link flap and waiting for idle - support MAC Merge layer - Other NICs: - sfc/ef100: add basic devlink support for ef100 - ionic: rx_push mode operation (writing descriptors via MMIO) - bnxt: use the auxiliary bus abstraction for RDMA - r8169: disable ASPM and reset bus in case of tx timeout - cpsw: support QSGMII mode for J721e CPSW9G - cpts: support pulse-per-second output - ngbe: add an mdio bus driver - usbnet: optimize usbnet_bh() by avoiding unnecessary queuing - r8152: handle devices with FW with NCM support - amd-xgbe: support 10Mbps, 2.5GbE speeds and rx-adaptation - virtio-net: support multi buffer XDP - virtio/vsock: replace virtio_vsock_pkt with sk_buff - tsnep: XDP support - Ethernet high-speed switches: - nVidia/Mellanox (mlxsw): - add support for latency TLV (in FW control messages) - Microchip (sparx5): - separate explicit and implicit traffic forwarding rules, make the implicit rules always active - add support for egress DSCP rewrite - IS0 VCAP support (Ingress Classification) - IS2 VCAP filters (protos, L3 addrs, L4 ports, flags, ToS etc.) - ES2 VCAP support (Egress Access Control) - support for Per-Stream Filtering and Policing (802.1Q, 8.6.5.1) - Ethernet embedded switches: - Marvell (mv88e6xxx): - add MAB (port auth) offload support - enable PTP receive for mv88e6390 - NXP (ocelot): - support MAC Merge layer - support for the the vsc7512 internal copper phys - Microchip: - lan9303: convert to PHYLINK - lan966x: support TC flower filter statistics - lan937x: PTP support for KSZ9563/KSZ8563 and LAN937x - lan937x: support Credit Based Shaper configuration - ksz9477: support Energy Efficient Ethernet - other: - qca8k: convert to regmap read/write API, use bulk operations - rswitch: Improve TX timestamp accuracy - Intel WiFi (iwlwifi): - EHT (Wi-Fi 7) rate reporting - STEP equalizer support: transfer some STEP (connection to radio on platforms with integrated wifi) related parameters from the BIOS to the firmware. - Qualcomm 802.11ax WiFi (ath11k): - IPQ5018 support - Fine Timing Measurement (FTM) responder role support - channel 177 support - MediaTek WiFi (mt76): - per-PHY LED support - mt7996: EHT (Wi-Fi 7) support - Wireless Ethernet Dispatch (WED) reset support - switch to using page pool allocator - RealTek WiFi (rtw89): - support new version of Bluetooth co-existance - Mobile: - rmnet: support TX aggregation" * tag 'net-next-6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next: (1872 commits) page_pool: add a comment explaining the fragment counter usage net: ethtool: fix __ethtool_dev_mm_supported() implementation ethtool: pse-pd: Fix double word in comments xsk: add linux/vmalloc.h to xsk.c sefltests: netdevsim: wait for devlink instance after netns removal selftest: fib_tests: Always cleanup before exit net/mlx5e: Align IPsec ASO result memory to be as required by hardware net/mlx5e: TC, Set CT miss to the specific ct action instance net/mlx5e: Rename CHAIN_TO_REG to MAPPED_OBJ_TO_REG net/mlx5: Refactor tc miss handling to a single function net/mlx5: Kconfig: Make tc offload depend on tc skb extension net/sched: flower: Support hardware miss to tc action net/sched: flower: Move filter handle initialization earlier net/sched: cls_api: Support hardware miss to tc action net/sched: Rename user cookie and act cookie sfc: fix builds without CONFIG_RTC_LIB sfc: clean up some inconsistent indentings net/mlx4_en: Introduce flexible array to silence overflow warning net: lan966x: Fix possible deadlock inside PTP net/ulp: Remove redundant ->clone() test in inet_clone_ulp(). ...
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+==========================================
+I915 VM_BIND feature design and use cases
+==========================================
+
+VM_BIND feature
+================
+DRM_I915_GEM_VM_BIND/UNBIND ioctls allows UMD to bind/unbind GEM buffer
+objects (BOs) or sections of a BOs at specified GPU virtual addresses on a
+specified address space (VM). These mappings (also referred to as persistent
+mappings) will be persistent across multiple GPU submissions (execbuf calls)
+issued by the UMD, without user having to provide a list of all required
+mappings during each submission (as required by older execbuf mode).
+
+The VM_BIND/UNBIND calls allow UMDs to request a timeline out fence for
+signaling the completion of bind/unbind operation.
+
+VM_BIND feature is advertised to user via I915_PARAM_VM_BIND_VERSION.
+User has to opt-in for VM_BIND mode of binding for an address space (VM)
+during VM creation time via I915_VM_CREATE_FLAGS_USE_VM_BIND extension.
+
+VM_BIND/UNBIND ioctl calls executed on different CPU threads concurrently are
+not ordered. Furthermore, parts of the VM_BIND/UNBIND operations can be done
+asynchronously, when valid out fence is specified.
+
+VM_BIND features include:
+
+* Multiple Virtual Address (VA) mappings can map to the same physical pages
+ of an object (aliasing).
+* VA mapping can map to a partial section of the BO (partial binding).
+* Support capture of persistent mappings in the dump upon GPU error.
+* Support for userptr gem objects (no special uapi is required for this).
+
+TLB flush consideration
+------------------------
+The i915 driver flushes the TLB for each submission and when an object's
+pages are released. The VM_BIND/UNBIND operation will not do any additional
+TLB flush. Any VM_BIND mapping added will be in the working set for subsequent
+submissions on that VM and will not be in the working set for currently running
+batches (which would require additional TLB flushes, which is not supported).
+
+Execbuf ioctl in VM_BIND mode
+-------------------------------
+A VM in VM_BIND mode will not support older execbuf mode of binding.
+The execbuf ioctl handling in VM_BIND mode differs significantly from the
+older execbuf2 ioctl (See struct drm_i915_gem_execbuffer2).
+Hence, a new execbuf3 ioctl has been added to support VM_BIND mode. (See
+struct drm_i915_gem_execbuffer3). The execbuf3 ioctl will not accept any
+execlist. Hence, no support for implicit sync. It is expected that the below
+work will be able to support requirements of object dependency setting in all
+use cases:
+
+"dma-buf: Add an API for exporting sync files"
+(https://lwn.net/Articles/859290/)
+
+The new execbuf3 ioctl only works in VM_BIND mode and the VM_BIND mode only
+works with execbuf3 ioctl for submission. All BOs mapped on that VM (through
+VM_BIND call) at the time of execbuf3 call are deemed required for that
+submission.
+
+The execbuf3 ioctl directly specifies the batch addresses instead of as
+object handles as in execbuf2 ioctl. The execbuf3 ioctl will also not
+support many of the older features like in/out/submit fences, fence array,
+default gem context and many more (See struct drm_i915_gem_execbuffer3).
+
+In VM_BIND mode, VA allocation is completely managed by the user instead of
+the i915 driver. Hence all VA assignment, eviction are not applicable in
+VM_BIND mode. Also, for determining object activeness, VM_BIND mode will not
+be using the i915_vma active reference tracking. It will instead use dma-resv
+object for that (See `VM_BIND dma_resv usage`_).
+
+So, a lot of existing code supporting execbuf2 ioctl, like relocations, VA
+evictions, vma lookup table, implicit sync, vma active reference tracking etc.,
+are not applicable for execbuf3 ioctl. Hence, all execbuf3 specific handling
+should be in a separate file and only functionalities common to these ioctls
+can be the shared code where possible.
+
+VM_PRIVATE objects
+-------------------
+By default, BOs can be mapped on multiple VMs and can also be dma-buf
+exported. Hence these BOs are referred to as Shared BOs.
+During each execbuf submission, the request fence must be added to the
+dma-resv fence list of all shared BOs mapped on the VM.
+
+VM_BIND feature introduces an optimization where user can create BO which
+is private to a specified VM via I915_GEM_CREATE_EXT_VM_PRIVATE flag during
+BO creation. Unlike Shared BOs, these VM private BOs can only be mapped on
+the VM they are private to and can't be dma-buf exported.
+All private BOs of a VM share the dma-resv object. Hence during each execbuf
+submission, they need only one dma-resv fence list updated. Thus, the fast
+path (where required mappings are already bound) submission latency is O(1)
+w.r.t the number of VM private BOs.
+
+VM_BIND locking hirarchy
+-------------------------
+The locking design here supports the older (execlist based) execbuf mode, the
+newer VM_BIND mode, the VM_BIND mode with GPU page faults and possible future
+system allocator support (See `Shared Virtual Memory (SVM) support`_).
+The older execbuf mode and the newer VM_BIND mode without page faults manages
+residency of backing storage using dma_fence. The VM_BIND mode with page faults
+and the system allocator support do not use any dma_fence at all.
+
+VM_BIND locking order is as below.
+
+1) Lock-A: A vm_bind mutex will protect vm_bind lists. This lock is taken in
+ vm_bind/vm_unbind ioctl calls, in the execbuf path and while releasing the
+ mapping.
+
+ In future, when GPU page faults are supported, we can potentially use a
+ rwsem instead, so that multiple page fault handlers can take the read side
+ lock to lookup the mapping and hence can run in parallel.
+ The older execbuf mode of binding do not need this lock.
+
+2) Lock-B: The object's dma-resv lock will protect i915_vma state and needs to
+ be held while binding/unbinding a vma in the async worker and while updating
+ dma-resv fence list of an object. Note that private BOs of a VM will all
+ share a dma-resv object.
+
+ The future system allocator support will use the HMM prescribed locking
+ instead.
+
+3) Lock-C: Spinlock/s to protect some of the VM's lists like the list of
+ invalidated vmas (due to eviction and userptr invalidation) etc.
+
+When GPU page faults are supported, the execbuf path do not take any of these
+locks. There we will simply smash the new batch buffer address into the ring and
+then tell the scheduler run that. The lock taking only happens from the page
+fault handler, where we take lock-A in read mode, whichever lock-B we need to
+find the backing storage (dma_resv lock for gem objects, and hmm/core mm for
+system allocator) and some additional locks (lock-D) for taking care of page
+table races. Page fault mode should not need to ever manipulate the vm lists,
+so won't ever need lock-C.
+
+VM_BIND LRU handling
+---------------------
+We need to ensure VM_BIND mapped objects are properly LRU tagged to avoid
+performance degradation. We will also need support for bulk LRU movement of
+VM_BIND objects to avoid additional latencies in execbuf path.
+
+The page table pages are similar to VM_BIND mapped objects (See
+`Evictable page table allocations`_) and are maintained per VM and needs to
+be pinned in memory when VM is made active (ie., upon an execbuf call with
+that VM). So, bulk LRU movement of page table pages is also needed.
+
+VM_BIND dma_resv usage
+-----------------------
+Fences needs to be added to all VM_BIND mapped objects. During each execbuf
+submission, they are added with DMA_RESV_USAGE_BOOKKEEP usage to prevent
+over sync (See enum dma_resv_usage). One can override it with either
+DMA_RESV_USAGE_READ or DMA_RESV_USAGE_WRITE usage during explicit object
+dependency setting.
+
+Note that DRM_I915_GEM_WAIT and DRM_I915_GEM_BUSY ioctls do not check for
+DMA_RESV_USAGE_BOOKKEEP usage and hence should not be used for end of batch
+check. Instead, the execbuf3 out fence should be used for end of batch check
+(See struct drm_i915_gem_execbuffer3).
+
+Also, in VM_BIND mode, use dma-resv apis for determining object activeness
+(See dma_resv_test_signaled() and dma_resv_wait_timeout()) and do not use the
+older i915_vma active reference tracking which is deprecated. This should be
+easier to get it working with the current TTM backend.
+
+Mesa use case
+--------------
+VM_BIND can potentially reduce the CPU overhead in Mesa (both Vulkan and Iris),
+hence improving performance of CPU-bound applications. It also allows us to
+implement Vulkan's Sparse Resources. With increasing GPU hardware performance,
+reducing CPU overhead becomes more impactful.
+
+
+Other VM_BIND use cases
+========================
+
+Long running Compute contexts
+------------------------------
+Usage of dma-fence expects that they complete in reasonable amount of time.
+Compute on the other hand can be long running. Hence it is appropriate for
+compute to use user/memory fence (See `User/Memory Fence`_) and dma-fence usage
+must be limited to in-kernel consumption only.
+
+Where GPU page faults are not available, kernel driver upon buffer invalidation
+will initiate a suspend (preemption) of long running context, finish the
+invalidation, revalidate the BO and then resume the compute context. This is
+done by having a per-context preempt fence which is enabled when someone tries
+to wait on it and triggers the context preemption.
+
+User/Memory Fence
+~~~~~~~~~~~~~~~~~~
+User/Memory fence is a <address, value> pair. To signal the user fence, the
+specified value will be written at the specified virtual address and wakeup the
+waiting process. User fence can be signaled either by the GPU or kernel async
+worker (like upon bind completion). User can wait on a user fence with a new
+user fence wait ioctl.
+
+Here is some prior work on this:
+https://patchwork.freedesktop.org/patch/349417/
+
+Low Latency Submission
+~~~~~~~~~~~~~~~~~~~~~~~
+Allows compute UMD to directly submit GPU jobs instead of through execbuf
+ioctl. This is made possible by VM_BIND is not being synchronized against
+execbuf. VM_BIND allows bind/unbind of mappings required for the directly
+submitted jobs.
+
+Debugger
+---------
+With debug event interface user space process (debugger) is able to keep track
+of and act upon resources created by another process (debugged) and attached
+to GPU via vm_bind interface.
+
+GPU page faults
+----------------
+GPU page faults when supported (in future), will only be supported in the
+VM_BIND mode. While both the older execbuf mode and the newer VM_BIND mode of
+binding will require using dma-fence to ensure residency, the GPU page faults
+mode when supported, will not use any dma-fence as residency is purely managed
+by installing and removing/invalidating page table entries.
+
+Page level hints settings
+--------------------------
+VM_BIND allows any hints setting per mapping instead of per BO. Possible hints
+include placement and atomicity. Sub-BO level placement hint will be even more
+relevant with upcoming GPU on-demand page fault support.
+
+Page level Cache/CLOS settings
+-------------------------------
+VM_BIND allows cache/CLOS settings per mapping instead of per BO.
+
+Evictable page table allocations
+---------------------------------
+Make pagetable allocations evictable and manage them similar to VM_BIND
+mapped objects. Page table pages are similar to persistent mappings of a
+VM (difference here are that the page table pages will not have an i915_vma
+structure and after swapping pages back in, parent page link needs to be
+updated).
+
+Shared Virtual Memory (SVM) support
+------------------------------------
+VM_BIND interface can be used to map system memory directly (without gem BO
+abstraction) using the HMM interface. SVM is only supported with GPU page
+faults enabled.
+
+VM_BIND UAPI
+=============
+
+.. kernel-doc:: Documentation/gpu/rfc/i915_vm_bind.h