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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 /tools/perf/Documentation/topdown.txt
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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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+Using TopDown metrics in user space
+-----------------------------------
+
+Intel CPUs (since Sandy Bridge and Silvermont) support a TopDown
+methodology to break down CPU pipeline execution into 4 bottlenecks:
+frontend bound, backend bound, bad speculation, retiring.
+
+For more details on Topdown see [1][5]
+
+Traditionally this was implemented by events in generic counters
+and specific formulas to compute the bottlenecks.
+
+perf stat --topdown implements this.
+
+Full Top Down includes more levels that can break down the
+bottlenecks further. This is not directly implemented in perf,
+but available in other tools that can run on top of perf,
+such as toplev[2] or vtune[3]
+
+New Topdown features in Ice Lake
+===============================
+
+With Ice Lake CPUs the TopDown metrics are directly available as
+fixed counters and do not require generic counters. This allows
+to collect TopDown always in addition to other events.
+
+% perf stat -a --topdown -I1000
+# time retiring bad speculation frontend bound backend bound
+ 1.001281330 23.0% 15.3% 29.6% 32.1%
+ 2.003009005 5.0% 6.8% 46.6% 41.6%
+ 3.004646182 6.7% 6.7% 46.0% 40.6%
+ 4.006326375 5.0% 6.4% 47.6% 41.0%
+ 5.007991804 5.1% 6.3% 46.3% 42.3%
+ 6.009626773 6.2% 7.1% 47.3% 39.3%
+ 7.011296356 4.7% 6.7% 46.2% 42.4%
+ 8.012951831 4.7% 6.7% 47.5% 41.1%
+...
+
+This also enables measuring TopDown per thread/process instead
+of only per core.
+
+Using TopDown through RDPMC in applications on Ice Lake
+======================================================
+
+For more fine grained measurements it can be useful to
+access the new directly from user space. This is more complicated,
+but drastically lowers overhead.
+
+On Ice Lake, there is a new fixed counter 3: SLOTS, which reports
+"pipeline SLOTS" (cycles multiplied by core issue width) and a
+metric register that reports slots ratios for the different bottleneck
+categories.
+
+The metrics counter is CPU model specific and is not available on older
+CPUs.
+
+Example code
+============
+
+Library functions to do the functionality described below
+is also available in libjevents [4]
+
+The application opens a group with fixed counter 3 (SLOTS) and any
+metric event, and allow user programs to read the performance counters.
+
+Fixed counter 3 is mapped to a pseudo event event=0x00, umask=04,
+so the perf_event_attr structure should be initialized with
+{ .config = 0x0400, .type = PERF_TYPE_RAW }
+The metric events are mapped to the pseudo event event=0x00, umask=0x8X.
+For example, the perf_event_attr structure can be initialized with
+{ .config = 0x8000, .type = PERF_TYPE_RAW } for Retiring metric event
+The Fixed counter 3 must be the leader of the group.
+
+#include <linux/perf_event.h>
+#include <sys/mman.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+/* Provide own perf_event_open stub because glibc doesn't */
+__attribute__((weak))
+int perf_event_open(struct perf_event_attr *attr, pid_t pid,
+ int cpu, int group_fd, unsigned long flags)
+{
+ return syscall(__NR_perf_event_open, attr, pid, cpu, group_fd, flags);
+}
+
+/* Open slots counter file descriptor for current task. */
+struct perf_event_attr slots = {
+ .type = PERF_TYPE_RAW,
+ .size = sizeof(struct perf_event_attr),
+ .config = 0x400,
+ .exclude_kernel = 1,
+};
+
+int slots_fd = perf_event_open(&slots, 0, -1, -1, 0);
+if (slots_fd < 0)
+ ... error ...
+
+/* Memory mapping the fd permits _rdpmc calls from userspace */
+void *slots_p = mmap(0, getpagesize(), PROT_READ, MAP_SHARED, slots_fd, 0);
+if (!slot_p)
+ .... error ...
+
+/*
+ * Open metrics event file descriptor for current task.
+ * Set slots event as the leader of the group.
+ */
+struct perf_event_attr metrics = {
+ .type = PERF_TYPE_RAW,
+ .size = sizeof(struct perf_event_attr),
+ .config = 0x8000,
+ .exclude_kernel = 1,
+};
+
+int metrics_fd = perf_event_open(&metrics, 0, -1, slots_fd, 0);
+if (metrics_fd < 0)
+ ... error ...
+
+/* Memory mapping the fd permits _rdpmc calls from userspace */
+void *metrics_p = mmap(0, getpagesize(), PROT_READ, MAP_SHARED, metrics_fd, 0);
+if (!metrics_p)
+ ... error ...
+
+Note: the file descriptors returned by the perf_event_open calls must be memory
+mapped to permit calls to the _rdpmd instruction. Permission may also be granted
+by writing the /sys/devices/cpu/rdpmc sysfs node.
+
+The RDPMC instruction (or _rdpmc compiler intrinsic) can now be used
+to read slots and the topdown metrics at different points of the program:
+
+#include <stdint.h>
+#include <x86intrin.h>
+
+#define RDPMC_FIXED (1 << 30) /* return fixed counters */
+#define RDPMC_METRIC (1 << 29) /* return metric counters */
+
+#define FIXED_COUNTER_SLOTS 3
+#define METRIC_COUNTER_TOPDOWN_L1_L2 0
+
+static inline uint64_t read_slots(void)
+{
+ return _rdpmc(RDPMC_FIXED | FIXED_COUNTER_SLOTS);
+}
+
+static inline uint64_t read_metrics(void)
+{
+ return _rdpmc(RDPMC_METRIC | METRIC_COUNTER_TOPDOWN_L1_L2);
+}
+
+Then the program can be instrumented to read these metrics at different
+points.
+
+It's not a good idea to do this with too short code regions,
+as the parallelism and overlap in the CPU program execution will
+cause too much measurement inaccuracy. For example instrumenting
+individual basic blocks is definitely too fine grained.
+
+_rdpmc calls should not be mixed with reading the metrics and slots counters
+through system calls, as the kernel will reset these counters after each system
+call.
+
+Decoding metrics values
+=======================
+
+The value reported by read_metrics() contains four 8 bit fields
+that represent a scaled ratio that represent the Level 1 bottleneck.
+All four fields add up to 0xff (= 100%)
+
+The binary ratios in the metric value can be converted to float ratios:
+
+#define GET_METRIC(m, i) (((m) >> (i*8)) & 0xff)
+
+/* L1 Topdown metric events */
+#define TOPDOWN_RETIRING(val) ((float)GET_METRIC(val, 0) / 0xff)
+#define TOPDOWN_BAD_SPEC(val) ((float)GET_METRIC(val, 1) / 0xff)
+#define TOPDOWN_FE_BOUND(val) ((float)GET_METRIC(val, 2) / 0xff)
+#define TOPDOWN_BE_BOUND(val) ((float)GET_METRIC(val, 3) / 0xff)
+
+/*
+ * L2 Topdown metric events.
+ * Available on Sapphire Rapids and later platforms.
+ */
+#define TOPDOWN_HEAVY_OPS(val) ((float)GET_METRIC(val, 4) / 0xff)
+#define TOPDOWN_BR_MISPREDICT(val) ((float)GET_METRIC(val, 5) / 0xff)
+#define TOPDOWN_FETCH_LAT(val) ((float)GET_METRIC(val, 6) / 0xff)
+#define TOPDOWN_MEM_BOUND(val) ((float)GET_METRIC(val, 7) / 0xff)
+
+and then converted to percent for printing.
+
+The ratios in the metric accumulate for the time when the counter
+is enabled. For measuring programs it is often useful to measure
+specific sections. For this it is needed to deltas on metrics.
+
+This can be done by scaling the metrics with the slots counter
+read at the same time.
+
+Then it's possible to take deltas of these slots counts
+measured at different points, and determine the metrics
+for that time period.
+
+ slots_a = read_slots();
+ metric_a = read_metrics();
+
+ ... larger code region ...
+
+ slots_b = read_slots()
+ metric_b = read_metrics()
+
+ # compute scaled metrics for measurement a
+ retiring_slots_a = GET_METRIC(metric_a, 0) * slots_a
+ bad_spec_slots_a = GET_METRIC(metric_a, 1) * slots_a
+ fe_bound_slots_a = GET_METRIC(metric_a, 2) * slots_a
+ be_bound_slots_a = GET_METRIC(metric_a, 3) * slots_a
+
+ # compute delta scaled metrics between b and a
+ retiring_slots = GET_METRIC(metric_b, 0) * slots_b - retiring_slots_a
+ bad_spec_slots = GET_METRIC(metric_b, 1) * slots_b - bad_spec_slots_a
+ fe_bound_slots = GET_METRIC(metric_b, 2) * slots_b - fe_bound_slots_a
+ be_bound_slots = GET_METRIC(metric_b, 3) * slots_b - be_bound_slots_a
+
+Later the individual ratios of L1 metric events for the measurement period can
+be recreated from these counts.
+
+ slots_delta = slots_b - slots_a
+ retiring_ratio = (float)retiring_slots / slots_delta
+ bad_spec_ratio = (float)bad_spec_slots / slots_delta
+ fe_bound_ratio = (float)fe_bound_slots / slots_delta
+ be_bound_ratio = (float)be_bound_slots / slota_delta
+
+ printf("Retiring %.2f%% Bad Speculation %.2f%% FE Bound %.2f%% BE Bound %.2f%%\n",
+ retiring_ratio * 100.,
+ bad_spec_ratio * 100.,
+ fe_bound_ratio * 100.,
+ be_bound_ratio * 100.);
+
+The individual ratios of L2 metric events for the measurement period can be
+recreated from L1 and L2 metric counters. (Available on Sapphire Rapids and
+later platforms)
+
+ # compute scaled metrics for measurement a
+ heavy_ops_slots_a = GET_METRIC(metric_a, 4) * slots_a
+ br_mispredict_slots_a = GET_METRIC(metric_a, 5) * slots_a
+ fetch_lat_slots_a = GET_METRIC(metric_a, 6) * slots_a
+ mem_bound_slots_a = GET_METRIC(metric_a, 7) * slots_a
+
+ # compute delta scaled metrics between b and a
+ heavy_ops_slots = GET_METRIC(metric_b, 4) * slots_b - heavy_ops_slots_a
+ br_mispredict_slots = GET_METRIC(metric_b, 5) * slots_b - br_mispredict_slots_a
+ fetch_lat_slots = GET_METRIC(metric_b, 6) * slots_b - fetch_lat_slots_a
+ mem_bound_slots = GET_METRIC(metric_b, 7) * slots_b - mem_bound_slots_a
+
+ slots_delta = slots_b - slots_a
+ heavy_ops_ratio = (float)heavy_ops_slots / slots_delta
+ light_ops_ratio = retiring_ratio - heavy_ops_ratio;
+
+ br_mispredict_ratio = (float)br_mispredict_slots / slots_delta
+ machine_clears_ratio = bad_spec_ratio - br_mispredict_ratio;
+
+ fetch_lat_ratio = (float)fetch_lat_slots / slots_delta
+ fetch_bw_ratio = fe_bound_ratio - fetch_lat_ratio;
+
+ mem_bound_ratio = (float)mem_bound_slots / slota_delta
+ core_bound_ratio = be_bound_ratio - mem_bound_ratio;
+
+ printf("Heavy Operations %.2f%% Light Operations %.2f%% "
+ "Branch Mispredict %.2f%% Machine Clears %.2f%% "
+ "Fetch Latency %.2f%% Fetch Bandwidth %.2f%% "
+ "Mem Bound %.2f%% Core Bound %.2f%%\n",
+ heavy_ops_ratio * 100.,
+ light_ops_ratio * 100.,
+ br_mispredict_ratio * 100.,
+ machine_clears_ratio * 100.,
+ fetch_lat_ratio * 100.,
+ fetch_bw_ratio * 100.,
+ mem_bound_ratio * 100.,
+ core_bound_ratio * 100.);
+
+Resetting metrics counters
+==========================
+
+Since the individual metrics are only 8bit they lose precision for
+short regions over time because the number of cycles covered by each
+fraction bit shrinks. So the counters need to be reset regularly.
+
+When using the kernel perf API the kernel resets on every read.
+So as long as the reading is at reasonable intervals (every few
+seconds) the precision is good.
+
+When using perf stat it is recommended to always use the -I option,
+with no longer interval than a few seconds
+
+ perf stat -I 1000 --topdown ...
+
+For user programs using RDPMC directly the counter can
+be reset explicitly using ioctl:
+
+ ioctl(perf_fd, PERF_EVENT_IOC_RESET, 0);
+
+This "opens" a new measurement period.
+
+A program using RDPMC for TopDown should schedule such a reset
+regularly, as in every few seconds.
+
+Limits on Ice Lake
+==================
+
+Four pseudo TopDown metric events are exposed for the end-users,
+topdown-retiring, topdown-bad-spec, topdown-fe-bound and topdown-be-bound.
+They can be used to collect the TopDown value under the following
+rules:
+- All the TopDown metric events must be in a group with the SLOTS event.
+- The SLOTS event must be the leader of the group.
+- The PERF_FORMAT_GROUP flag must be applied for each TopDown metric
+ events
+
+The SLOTS event and the TopDown metric events can be counting members of
+a sampling read group. Since the SLOTS event must be the leader of a TopDown
+group, the second event of the group is the sampling event.
+For example, perf record -e '{slots, $sampling_event, topdown-retiring}:S'
+
+Extension on Sapphire Rapids Server
+===================================
+The metrics counter is extended to support TMA method level 2 metrics.
+The lower half of the register is the TMA level 1 metrics (legacy).
+The upper half is also divided into four 8-bit fields for the new level 2
+metrics. Four more TopDown metric events are exposed for the end-users,
+topdown-heavy-ops, topdown-br-mispredict, topdown-fetch-lat and
+topdown-mem-bound.
+
+Each of the new level 2 metrics in the upper half is a subset of the
+corresponding level 1 metric in the lower half. Software can deduce the
+other four level 2 metrics by subtracting corresponding metrics as below.
+
+ Light_Operations = Retiring - Heavy_Operations
+ Machine_Clears = Bad_Speculation - Branch_Mispredicts
+ Fetch_Bandwidth = Frontend_Bound - Fetch_Latency
+ Core_Bound = Backend_Bound - Memory_Bound
+
+
+[1] https://software.intel.com/en-us/top-down-microarchitecture-analysis-method-win
+[2] https://github.com/andikleen/pmu-tools/wiki/toplev-manual
+[3] https://software.intel.com/en-us/intel-vtune-amplifier-xe
+[4] https://github.com/andikleen/pmu-tools/tree/master/jevents
+[5] https://sites.google.com/site/analysismethods/yasin-pubs