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author | 2023-02-21 18:24:12 -0800 | |
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committer | 2023-02-21 18:24:12 -0800 | |
commit | 5b7c4cabbb65f5c469464da6c5f614cbd7f730f2 (patch) | |
tree | cc5c2d0a898769fd59549594fedb3ee6f84e59a0 /Documentation/arm/vlocks.rst | |
download | linux-5b7c4cabbb65f5c469464da6c5f614cbd7f730f2.tar.gz linux-5b7c4cabbb65f5c469464da6c5f614cbd7f730f2.zip |
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().
...
Diffstat (limited to 'Documentation/arm/vlocks.rst')
-rw-r--r-- | Documentation/arm/vlocks.rst | 212 |
1 files changed, 212 insertions, 0 deletions
diff --git a/Documentation/arm/vlocks.rst b/Documentation/arm/vlocks.rst new file mode 100644 index 000000000..a40a17421 --- /dev/null +++ b/Documentation/arm/vlocks.rst @@ -0,0 +1,212 @@ +====================================== +vlocks for Bare-Metal Mutual Exclusion +====================================== + +Voting Locks, or "vlocks" provide a simple low-level mutual exclusion +mechanism, with reasonable but minimal requirements on the memory +system. + +These are intended to be used to coordinate critical activity among CPUs +which are otherwise non-coherent, in situations where the hardware +provides no other mechanism to support this and ordinary spinlocks +cannot be used. + + +vlocks make use of the atomicity provided by the memory system for +writes to a single memory location. To arbitrate, every CPU "votes for +itself", by storing a unique number to a common memory location. The +final value seen in that memory location when all the votes have been +cast identifies the winner. + +In order to make sure that the election produces an unambiguous result +in finite time, a CPU will only enter the election in the first place if +no winner has been chosen and the election does not appear to have +started yet. + + +Algorithm +--------- + +The easiest way to explain the vlocks algorithm is with some pseudo-code:: + + + int currently_voting[NR_CPUS] = { 0, }; + int last_vote = -1; /* no votes yet */ + + bool vlock_trylock(int this_cpu) + { + /* signal our desire to vote */ + currently_voting[this_cpu] = 1; + if (last_vote != -1) { + /* someone already volunteered himself */ + currently_voting[this_cpu] = 0; + return false; /* not ourself */ + } + + /* let's suggest ourself */ + last_vote = this_cpu; + currently_voting[this_cpu] = 0; + + /* then wait until everyone else is done voting */ + for_each_cpu(i) { + while (currently_voting[i] != 0) + /* wait */; + } + + /* result */ + if (last_vote == this_cpu) + return true; /* we won */ + return false; + } + + bool vlock_unlock(void) + { + last_vote = -1; + } + + +The currently_voting[] array provides a way for the CPUs to determine +whether an election is in progress, and plays a role analogous to the +"entering" array in Lamport's bakery algorithm [1]. + +However, once the election has started, the underlying memory system +atomicity is used to pick the winner. This avoids the need for a static +priority rule to act as a tie-breaker, or any counters which could +overflow. + +As long as the last_vote variable is globally visible to all CPUs, it +will contain only one value that won't change once every CPU has cleared +its currently_voting flag. + + +Features and limitations +------------------------ + + * vlocks are not intended to be fair. In the contended case, it is the + _last_ CPU which attempts to get the lock which will be most likely + to win. + + vlocks are therefore best suited to situations where it is necessary + to pick a unique winner, but it does not matter which CPU actually + wins. + + * Like other similar mechanisms, vlocks will not scale well to a large + number of CPUs. + + vlocks can be cascaded in a voting hierarchy to permit better scaling + if necessary, as in the following hypothetical example for 4096 CPUs:: + + /* first level: local election */ + my_town = towns[(this_cpu >> 4) & 0xf]; + I_won = vlock_trylock(my_town, this_cpu & 0xf); + if (I_won) { + /* we won the town election, let's go for the state */ + my_state = states[(this_cpu >> 8) & 0xf]; + I_won = vlock_lock(my_state, this_cpu & 0xf)); + if (I_won) { + /* and so on */ + I_won = vlock_lock(the_whole_country, this_cpu & 0xf]; + if (I_won) { + /* ... */ + } + vlock_unlock(the_whole_country); + } + vlock_unlock(my_state); + } + vlock_unlock(my_town); + + +ARM implementation +------------------ + +The current ARM implementation [2] contains some optimisations beyond +the basic algorithm: + + * By packing the members of the currently_voting array close together, + we can read the whole array in one transaction (providing the number + of CPUs potentially contending the lock is small enough). This + reduces the number of round-trips required to external memory. + + In the ARM implementation, this means that we can use a single load + and comparison:: + + LDR Rt, [Rn] + CMP Rt, #0 + + ...in place of code equivalent to:: + + LDRB Rt, [Rn] + CMP Rt, #0 + LDRBEQ Rt, [Rn, #1] + CMPEQ Rt, #0 + LDRBEQ Rt, [Rn, #2] + CMPEQ Rt, #0 + LDRBEQ Rt, [Rn, #3] + CMPEQ Rt, #0 + + This cuts down on the fast-path latency, as well as potentially + reducing bus contention in contended cases. + + The optimisation relies on the fact that the ARM memory system + guarantees coherency between overlapping memory accesses of + different sizes, similarly to many other architectures. Note that + we do not care which element of currently_voting appears in which + bits of Rt, so there is no need to worry about endianness in this + optimisation. + + If there are too many CPUs to read the currently_voting array in + one transaction then multiple transations are still required. The + implementation uses a simple loop of word-sized loads for this + case. The number of transactions is still fewer than would be + required if bytes were loaded individually. + + + In principle, we could aggregate further by using LDRD or LDM, but + to keep the code simple this was not attempted in the initial + implementation. + + + * vlocks are currently only used to coordinate between CPUs which are + unable to enable their caches yet. This means that the + implementation removes many of the barriers which would be required + when executing the algorithm in cached memory. + + packing of the currently_voting array does not work with cached + memory unless all CPUs contending the lock are cache-coherent, due + to cache writebacks from one CPU clobbering values written by other + CPUs. (Though if all the CPUs are cache-coherent, you should be + probably be using proper spinlocks instead anyway). + + + * The "no votes yet" value used for the last_vote variable is 0 (not + -1 as in the pseudocode). This allows statically-allocated vlocks + to be implicitly initialised to an unlocked state simply by putting + them in .bss. + + An offset is added to each CPU's ID for the purpose of setting this + variable, so that no CPU uses the value 0 for its ID. + + +Colophon +-------- + +Originally created and documented by Dave Martin for Linaro Limited, for +use in ARM-based big.LITTLE platforms, with review and input gratefully +received from Nicolas Pitre and Achin Gupta. Thanks to Nicolas for +grabbing most of this text out of the relevant mail thread and writing +up the pseudocode. + +Copyright (C) 2012-2013 Linaro Limited +Distributed under the terms of Version 2 of the GNU General Public +License, as defined in linux/COPYING. + + +References +---------- + +[1] Lamport, L. "A New Solution of Dijkstra's Concurrent Programming + Problem", Communications of the ACM 17, 8 (August 1974), 453-455. + + https://en.wikipedia.org/wiki/Lamport%27s_bakery_algorithm + +[2] linux/arch/arm/common/vlock.S, www.kernel.org. |