mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-08-22 17:01:14 +00:00
e23db805da
This is a tool that is intended to work around the fact that the preemptoff, irqsoff, and preemptirqsoff tracers only work in overwrite mode. The idea is to act randomly in such a way that we do not systematically lose any latencies, so that if enough testing is done, all latencies will be captured. If the same burst of latencies is repeated, then sooner or later we will have captured all the latencies. It also works with the wakeup_dl, wakeup_rt, and wakeup tracers. However, in that case it is probably not useful to use the random sleep functionality. The reason why it may be desirable to catch all latencies with a long test campaign is that for some organizations, it's necessary to test the kernel in the field and not practical for developers to work iteratively with field testers. Because of cost and project schedules it is not possible to start a new test campaign every time a latency problem has been fixed. It uses inotify to detect changes to /sys/kernel/tracing/trace. When a latency is detected, it will either sleep or print immediately, depending on a function that act as an unfair coin toss. If immediate print is chosen, it means that we open /sys/kernel/tracing/trace and thereby cause a blackout period that will hide any subsequent latencies. If sleep is chosen, it means that we wait before opening /sys/kernel/tracing/trace, by default for 1000 ms, to see if there is another latency during this period. If there is, then we will lose the previous latency. The coin will be tossed again with a different probability, and we will either print the new latency, or possibly a subsequent one. The probability for the unfair coin toss is chosen so that there is equal probability to obtain any of the latencies in a burst. However, this assumes that we make an assumption of how many latencies there can be. By default the program assumes that there are no more than 2 latencies in a burst, the probability of immediate printout will be: 1/2 and 1 Thus, the probability of getting each of the two latencies will be 1/2. If we ever find that there is more than one latency in a series, meaning that we reach the probability of 1, then the table will be expanded to: 1/3, 1/2, and 1 Thus, we assume that there are no more than three latencies and each with a probability of 1/3 of being captured. If the probability of 1 is reached in the new table, that is we see more than two closely occurring latencies, then the table will again be extended, and so on. On my systems, it seems like this scheme works fairly well, as long as the latencies we trace are long enough, 300 us seems to be enough. This userspace program receive the inotify event at the end of a latency, and it has time until the end of the next latency to react, that is to open /sys/kernel/tracing/trace. Thus, if we trace latencies that are >300 us, then we have at least 300 us to react. The minimum latency will of course not be 300 us on all systems, it will depend on the hardware, kernel version, workload and configuration. Example usage: In one shell, give the following command: sudo latency-collector -rvv -t preemptirqsoff -s 2000 -a 3 This will trace latencies > 2000us with the preemptirqsoff tracer, using random sleep with maximum verbosity, with a probability table initialized to a size of 3. In another shell, generate a few bursts of latencies: root@host:~# modprobe preemptirq_delay_test delay=3000 test_mode=alternate burst_size=3 root@host:~# echo 1 > /sys/kernel/preemptirq_delay_test/trigger root@host:~# echo 1 > /sys/kernel/preemptirq_delay_test/trigger root@host:~# echo 1 > /sys/kernel/preemptirq_delay_test/trigger root@host:~# echo 1 > /sys/kernel/preemptirq_delay_test/trigger If all goes well, you should be getting stack traces that shows all the different latencies, i.e. you should see all the three functions preemptirqtest_0, preemptirqtest_1, preemptirqtest_2 in the stack traces. Link: https://lkml.kernel.org/r/20210212134421.172750-2-Viktor.Rosendahl@bmw.de Signed-off-by: Viktor Rosendahl <Viktor.Rosendahl@bmw.de> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
191 lines
6.2 KiB
Makefile
191 lines
6.2 KiB
Makefile
# SPDX-License-Identifier: GPL-2.0
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# Some of the tools (perf) use same make variables
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# as in kernel build.
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export srctree=
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export objtree=
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include scripts/Makefile.include
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help:
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@echo 'Possible targets:'
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@echo ''
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@echo ' acpi - ACPI tools'
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@echo ' bpf - misc BPF tools'
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@echo ' cgroup - cgroup tools'
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@echo ' cpupower - a tool for all things x86 CPU power'
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@echo ' debugging - tools for debugging'
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@echo ' firewire - the userspace part of nosy, an IEEE-1394 traffic sniffer'
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@echo ' firmware - Firmware tools'
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@echo ' freefall - laptop accelerometer program for disk protection'
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@echo ' gpio - GPIO tools'
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@echo ' hv - tools used when in Hyper-V clients'
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@echo ' iio - IIO tools'
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@echo ' intel-speed-select - Intel Speed Select tool'
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@echo ' kvm_stat - top-like utility for displaying kvm statistics'
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@echo ' leds - LEDs tools'
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@echo ' liblockdep - user-space wrapper for kernel locking-validator'
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@echo ' objtool - an ELF object analysis tool'
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@echo ' pci - PCI tools'
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@echo ' perf - Linux performance measurement and analysis tool'
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@echo ' selftests - various kernel selftests'
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@echo ' bootconfig - boot config tool'
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@echo ' spi - spi tools'
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@echo ' tmon - thermal monitoring and tuning tool'
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@echo ' tracing - misc tracing tools'
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@echo ' turbostat - Intel CPU idle stats and freq reporting tool'
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@echo ' usb - USB testing tools'
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@echo ' virtio - vhost test module'
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@echo ' vm - misc vm tools'
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@echo ' wmi - WMI interface examples'
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@echo ' x86_energy_perf_policy - Intel energy policy tool'
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@echo ''
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@echo 'You can do:'
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@echo ' $$ make -C tools/ <tool>_install'
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@echo ''
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@echo ' from the kernel command line to build and install one of'
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@echo ' the tools above'
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@echo ''
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@echo ' $$ make tools/all'
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@echo ''
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@echo ' builds all tools.'
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@echo ''
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@echo ' $$ make tools/install'
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@echo ''
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@echo ' installs all tools.'
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@echo ''
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@echo 'Cleaning targets:'
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@echo ''
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@echo ' all of the above with the "_clean" string appended cleans'
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@echo ' the respective build directory.'
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@echo ' clean: a summary clean target to clean _all_ folders'
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acpi: FORCE
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$(call descend,power/$@)
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cpupower: FORCE
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$(call descend,power/$@)
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cgroup firewire hv guest bootconfig spi usb virtio vm bpf iio gpio objtool leds wmi pci firmware debugging tracing: FORCE
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$(call descend,$@)
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bpf/%: FORCE
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$(call descend,$@)
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liblockdep: FORCE
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$(call descend,lib/lockdep)
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libapi: FORCE
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$(call descend,lib/api)
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# The perf build does not follow the descend function setup,
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# invoking it via it's own make rule.
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PERF_O = $(if $(O),$(O)/tools/perf,)
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perf: FORCE
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$(Q)mkdir -p $(PERF_O) .
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$(Q)$(MAKE) --no-print-directory -C perf O=$(PERF_O) subdir=
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selftests: FORCE
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$(call descend,testing/$@)
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turbostat x86_energy_perf_policy intel-speed-select: FORCE
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$(call descend,power/x86/$@)
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tmon: FORCE
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$(call descend,thermal/$@)
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freefall: FORCE
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$(call descend,laptop/$@)
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kvm_stat: FORCE
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$(call descend,kvm/$@)
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all: acpi cgroup cpupower gpio hv firewire liblockdep \
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perf selftests bootconfig spi turbostat usb \
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virtio vm bpf x86_energy_perf_policy \
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tmon freefall iio objtool kvm_stat wmi \
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pci debugging tracing
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acpi_install:
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$(call descend,power/$(@:_install=),install)
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cpupower_install:
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$(call descend,power/$(@:_install=),install)
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cgroup_install firewire_install gpio_install hv_install iio_install perf_install bootconfig_install spi_install usb_install virtio_install vm_install bpf_install objtool_install wmi_install pci_install debugging_install tracing_install:
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$(call descend,$(@:_install=),install)
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liblockdep_install:
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$(call descend,lib/lockdep,install)
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selftests_install:
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$(call descend,testing/$(@:_install=),install)
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turbostat_install x86_energy_perf_policy_install intel-speed-select_install:
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$(call descend,power/x86/$(@:_install=),install)
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tmon_install:
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$(call descend,thermal/$(@:_install=),install)
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freefall_install:
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$(call descend,laptop/$(@:_install=),install)
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kvm_stat_install:
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$(call descend,kvm/$(@:_install=),install)
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install: acpi_install cgroup_install cpupower_install gpio_install \
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hv_install firewire_install iio_install liblockdep_install \
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perf_install selftests_install turbostat_install usb_install \
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virtio_install vm_install bpf_install x86_energy_perf_policy_install \
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tmon_install freefall_install objtool_install kvm_stat_install \
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wmi_install pci_install debugging_install intel-speed-select_install \
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tracing_install
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acpi_clean:
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$(call descend,power/acpi,clean)
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cpupower_clean:
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$(call descend,power/cpupower,clean)
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cgroup_clean hv_clean firewire_clean bootconfig_clean spi_clean usb_clean virtio_clean vm_clean wmi_clean bpf_clean iio_clean gpio_clean objtool_clean leds_clean pci_clean firmware_clean debugging_clean tracing_clean:
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$(call descend,$(@:_clean=),clean)
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liblockdep_clean:
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$(call descend,lib/lockdep,clean)
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libapi_clean:
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$(call descend,lib/api,clean)
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libbpf_clean:
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$(call descend,lib/bpf,clean)
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libsubcmd_clean:
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$(call descend,lib/subcmd,clean)
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perf_clean:
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$(Q)mkdir -p $(PERF_O) .
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$(Q)$(MAKE) --no-print-directory -C perf O=$(PERF_O) subdir= clean
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selftests_clean:
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$(call descend,testing/$(@:_clean=),clean)
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turbostat_clean x86_energy_perf_policy_clean intel-speed-select_clean:
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$(call descend,power/x86/$(@:_clean=),clean)
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tmon_clean:
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$(call descend,thermal/tmon,clean)
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freefall_clean:
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$(call descend,laptop/freefall,clean)
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build_clean:
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$(call descend,build,clean)
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clean: acpi_clean cgroup_clean cpupower_clean hv_clean firewire_clean \
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perf_clean selftests_clean turbostat_clean bootconfig_clean spi_clean usb_clean virtio_clean \
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vm_clean bpf_clean iio_clean x86_energy_perf_policy_clean tmon_clean \
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freefall_clean build_clean libbpf_clean libsubcmd_clean liblockdep_clean \
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gpio_clean objtool_clean leds_clean wmi_clean pci_clean firmware_clean debugging_clean \
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intel-speed-select_clean tracing_clean
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.PHONY: FORCE
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