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From:   Alexandru Elisei <alexandru.elisei@arm.com>
To:     linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Cc:     maz@kernel.org, will@kernel.org, catalin.marinas@arm.com,
        mark.rutland@arm.com
Subject: [PATCH v5 0/7] arm_pmu: Use NMI for perf interrupt
Date:   Wed, 17 Jun 2020 12:38:44 +0100
Message-Id: <20200617113851.607706-1-alexandru.elisei@arm.com>
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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