The series makes the arm_pmu driver use NMIs for the perf interrupt when
NMIs are available on the platform (currently, only arm64 + GICv3). To make
it easier to play with the patches, I've pushed a branch at [1]:
$ git clone -b pmu-nmi-v5 git://linux-arm.org/linux-ae
I've tested the series on an espressobin v7*. These are the results of
running perf record -a -- sleep 60:
1. Without the patches:
12.68% [k] _raw_spin_unlock_irq
11.08% [k] arch_cpu_idle
7.86% [k] _raw_spin_unlock_irqrestore
6.05% [k] arch_counter_get_cntpct
2.86% [k] __softirqentry_text_start
2.33% [k] tick_nohz_idle_exit
[..]
2. Using NMIs:
19.45% [k] arch_counter_get_cntpct
5.14% [k] __delay
3.32% [k] wait_for_xmitr
1.99% [k] ktime_get
1.00% [k] _raw_write_lock_irqsave
1.00% [.] avahi_escape_label
[..]
When running perf record -a -- iperf3 -c 127.0.0.1 -t 60:
1. Without the patches:
24.70% [k] __arch_copy_from_user
21.77% [k] __arch_copy_to_user
5.21% [k] _raw_spin_unlock_irq
2.86% [k] _raw_spin_unlock_irqrestore
1.99% [k] __free_pages_ok
1.61% [k] arch_cpu_idle
[..]
2. Using NMIs:
23.84% [k] __arch_copy_from_user
23.44% [k] __arch_copy_to_user
1.23% [k] get_page_from_freelist
1.16% [k] tcp_ack
0.80% [k] __free_pages_ok
0.78% [k] tcp_sendmsg_locked
[..]
I've ran the same tests in a VM when both host+guest use NMIs, and when
neither use them. All of these tests were also ran on the model. Similar
results in all cases.
* All the firmware versions for espressobin v7 that I've tried clear
SCR_EL3.FIQ, which means that NMIs don't work. To make them work on the
board, I modified the GICv3 driver. That's why I would really appreciate
someone testing this series on a board where NMIs work without any GIC
changes.
Summary of the patches:
* Patch 1 is a fix for a bug that Julien found during the review for v4.
* Patches 2 and 3 remove locking from arm64 perf event code.
* Patches 4 and 5 makes the arm64 PMU interrupt handler NMI safe.
* Patches 6 and 7 enable the use of NMIs on arm64 with a GICv3 irqchip.
Changes since v4 [2]:
- Rebased on top of v5.8-rc1 and dropped the Tested-by tags because it's
been almost a year since the series has been tested.
- Dropped patch 3 because I couldn't find any instance where
armv7pmu_read_counter() was called with interrupts enabled. I've also
tested this by running several instances of perf for a few hours, and the
function was called every time with interrupts disabled.
- Dropped patches 4 and 5 because the tradeoff wasn't worth it in my
opinion: the irq handler was slower all the time (because it
saved/restored the counter select register), in exchange for being
slightly faster on the rare ocassions when it triggered at the beginning
of the critical sections.
- Minor changes here and there to address review comments.
Changes since v3 [3]:
- Added tags
- Fix build issue for perf_event_v6
- Don't disable preemption in pmu->enable()
- Always rely on IPI_IRQ_WORK to run the queued work
- Fixed typos + cleanups
Changes since v2 [4]:
- Rebased on recent linux-next (next-20190708)
- Fixed a number of bugs with indices (reported by Wei)
- Minor style fixes
Changes since v1 [5]:
- Rebased on v5.1-rc1
- Pseudo-NMI has changed a lot since then, use the (now merged) NMI API
- Remove locking from armv7 perf_event
- Use locking only in armv6 perf_event
- Use direct counter/type registers insted of selector register for armv8
[1]
http://www.linux-arm.org/git?p=linux-ae.git;a=shortlog;h=refs/heads/pmu-nmi-v5
[2] https://lists.infradead.org/pipermail/linux-arm-kernel/2019-July/666824.html
[3] https://lists.infradead.org/pipermail/linux-arm-kernel/2019-July/665339.html
[4]
https://lists.infradead.org/pipermail/linux-arm-kernel/2019-March/640536.html
[5]
https://lists.infradead.org/pipermail/linux-arm-kernel/2018-January/554611.html
Alexandru Elisei (1):
arm64: perf: Add missing ISB in armv8pmu_enable_event()
Julien Thierry (5):
arm64: perf: Remove PMU locking
arm64: perf: Defer irq_work to IPI_IRQ_WORK
arm64: kvm: pmu: Make overflow handler NMI safe
arm_pmu: Introduce pmu_irq_ops
arm_pmu: arm64: Use NMIs for PMU
Mark Rutland (1):
arm64: perf: Avoid PMXEV* indirection
arch/arm64/kernel/perf_event.c | 138 ++++++++++++++++++++------------
arch/arm64/kvm/pmu-emul.c | 25 +++++-
drivers/perf/arm_pmu.c | 142 ++++++++++++++++++++++++++++-----
include/kvm/arm_pmu.h | 1 +
4 files changed, 235 insertions(+), 71 deletions(-)
--
2.27.0
