Re: [PATCH 3/3] arm64: use runtime constant to optimize handle_arch_irq access

[Jisheng Zhang <jszhang@kernel.org>]

On Fri, Feb 20, 2026 at 12:34:14PM +0000, Leo Yan wrote:
> Hi Jisheng,

Hi Leo,

> 
> On Fri, Feb 20, 2026 at 05:09:22PM +0800, Jisheng Zhang wrote:
> > Currently, on arm64 platforms, the handle_arch_irq is a pointer which
> > is set during booting, and every irq processing needs to access it,
> > so it sits in hot code path. We can use the runtime constant mechanism
> > which was introduced by Linus to speed up its accessing.
> > 
> > Tested on Quad CA55 platform, the perf sched benchmark is improved
> > by ~6.5%
> 
> 6.5% is a quite high margin, especially for only one pointer's change.
> Maybe it is good to share more info for which compiler you are using,
> how you tested and the detailed results.

Sure. 
aarch64-linux-gnu-gcc version 15.2.0

my kernel defconfig is a minimal arm64 version which disables most
drivers, only keep timer, gic, pll/clk, uart, regulator and i2c controller
The reason is to avoid OS noise as much as possible.
It's also put at the end of the email for reference.

testing cmd:
perf bench sched pipe

testing steps:
booting into a buildroot minimal initramfs
force cpufreq governor as performance
run above cmd

testing resuls:
before the patch:
9.471988 usecs/op
  105574 ops/sec

after the patch:
8.896280 usecs/op
  112406 ops/sec

(112406 - 105574) * 100 / 105574 = ~6.5 %

Let me know if you need more details


> 
> I played a bit on my juno board on CA73 cores with the command:

IIRC, Juno is powered by a big.little SoC, then we need to ensure
the benchmark is always running on big or little cores when testing, to
ensure apple to apple comparison.

I also have a CA73 platform, but can't access it now. I'll test the
patch next week.
> 
>   perf bench sched all
> 
> Run 3 iterations, and measures three metrics (messaging/pipe/seccomp)
> and results in seconds. Less is better.
> 
>   +---------------------+--------+--------+--------+--------+
>   |Without change       |   run1 |   run2 |   run3 |    avg |
>   +---------------------+--------+--------+--------+--------+
>   |messaging (sec)      |  4.546 |  4.508 |  4.591 |  4.548 |
>   |pipe (sec)           | 24.258 | 24.224 | 24.017 | 24.166 |
>   |seccomp-notify (sec) | 48.393 | 48.457 | 48.232 | 48.361 |
>   +---------------------+--------+--------+--------+--------+
> 
>   +---------------------+--------+--------+--------+--------+--------+
>   |With change          |   run1 |   run2 |   run3 |    avg |   diff |
>   +---------------------+--------+--------+--------+--------+--------+
>   |messaging (sec)      |  4.493 |  4.523 |  4.556 |  4.524 | +0.52% |
>   |pipe (sec)           | 23.159 | 23.702 | 28.649 | 25.170 | -4.15% |

If you check the result, this result variance is abnormal, it means
your OS is noiser.

>   |seccomp-notify (sec) | 46.848 | 46.938 | 46.973 | 46.920 | +2.98% |
>   +---------------------+--------+--------+--------+--------+--------+
> 
> With this patch, the messaging test shows a minor improvement (0.52%).
> 
> The pipe test performs worse (-4.15%) after applying the patch. However,
> one positive signal is that the minimum latency is 23.159, which is
> lower than without the change (24.017).

The perf bench is sensitive to OS noise, so I disable most devices, only
uart, timer, irq chip, i2c and regulator is kept,  and stop all daemons
only keep a usespace process bash shell.

defconfig for reference:

# CONFIG_LOCALVERSION_AUTO is not set
CONFIG_SYSVIPC=y
CONFIG_NO_HZ_IDLE=y
CONFIG_HIGH_RES_TIMERS=y
CONFIG_PREEMPT=y
# CONFIG_CPU_ISOLATION is not set
CONFIG_BLK_DEV_INITRD=y
# CONFIG_RD_GZIP is not set
# CONFIG_RD_BZIP2 is not set
# CONFIG_RD_LZMA is not set
# CONFIG_RD_XZ is not set
# CONFIG_RD_LZO is not set
# CONFIG_RD_LZ4 is not set
# CONFIG_INITRAMFS_PRESERVE_MTIME is not set
CONFIG_EXPERT=y
# CONFIG_UID16 is not set
# CONFIG_SYSFS_SYSCALL is not set
CONFIG_PROFILING=y
CONFIG_ARCH_BERLIN=y
# CONFIG_ARM64_ERRATUM_826319 is not set
# CONFIG_ARM64_ERRATUM_827319 is not set
# CONFIG_ARM64_ERRATUM_824069 is not set
# CONFIG_ARM64_ERRATUM_819472 is not set
# CONFIG_ARM64_ERRATUM_832075 is not set
# CONFIG_ARM64_ERRATUM_845719 is not set
# CONFIG_ARM64_ERRATUM_843419 is not set
# CONFIG_ARM64_ERRATUM_1418040 is not set
# CONFIG_ARM64_ERRATUM_1165522 is not set
# CONFIG_ARM64_ERRATUM_1463225 is not set
# CONFIG_CAVIUM_ERRATUM_22375 is not set
# CONFIG_CAVIUM_ERRATUM_23154 is not set
# CONFIG_CAVIUM_ERRATUM_27456 is not set
# CONFIG_CAVIUM_ERRATUM_30115 is not set
# CONFIG_CAVIUM_TX2_ERRATUM_219 is not set
# CONFIG_FUJITSU_ERRATUM_010001 is not set
# CONFIG_HISILICON_ERRATUM_161600802 is not set
# CONFIG_QCOM_FALKOR_ERRATUM_1003 is not set
# CONFIG_QCOM_FALKOR_ERRATUM_1009 is not set
# CONFIG_QCOM_QDF2400_ERRATUM_0065 is not set
# CONFIG_QCOM_FALKOR_ERRATUM_E1041 is not set
# CONFIG_SOCIONEXT_SYNQUACER_PREITS is not set
CONFIG_NR_CPUS=4
CONFIG_HOTPLUG_CPU=y
CONFIG_HZ_100=y
# CONFIG_UNMAP_KERNEL_AT_EL0 is not set
CONFIG_COMPAT=y
CONFIG_ARMV8_DEPRECATED=y
CONFIG_SWP_EMULATION=y
CONFIG_CP15_BARRIER_EMULATION=y
CONFIG_SETEND_EMULATION=y
# CONFIG_ARM64_HW_AFDBM is not set
# CONFIG_ARM64_PTR_AUTH is not set
# CONFIG_ARM64_AMU_EXTN is not set
# CONFIG_ARM64_SVE is not set
# CONFIG_EFI is not set
# CONFIG_SUSPEND is not set
CONFIG_CPU_IDLE=y
CONFIG_CPU_IDLE_GOV_TEO=y
CONFIG_ARM_PSCI_CPUIDLE=y
CONFIG_CPU_FREQ=y
CONFIG_CPU_FREQ_GOV_USERSPACE=y
CONFIG_CPUFREQ_DT=y
CONFIG_JUMP_LABEL=y
# CONFIG_VMAP_STACK is not set
# CONFIG_BLOCK is not set
# CONFIG_COMPAT_BRK is not set
# CONFIG_COMPACTION is not set
CONFIG_CMA=y
# CONFIG_ZONE_DMA32 is not set
# CONFIG_VM_EVENT_COUNTERS is not set
CONFIG_SYNA_DOLPHIN_PLL=y
CONFIG_SYNA_CLK_BASE=y
CONFIG_SYNA_MYNA2_CLK=y
CONFIG_PINCTRL_MYNA2=y
CONFIG_USB_DWC3_SYNA=y
# CONFIG_SYNAPTICS_PCIE is not set
CONFIG_REGULATOR_HL7593=y
CONFIG_PHY_SYNA_USB=y
# CONFIG_SYNAPTICS_I2C is not set
CONFIG_BERLIN_CHIPID=y
CONFIG_BERLIN_AXI_METER=y
# CONFIG_SYNAPTICS_NET is not set
# CONFIG_SYNAPTICS_VIDEO is not set
# CONFIG_SYNAPTICS_SOUND is not set
# CONFIG_SYNAPTICS_DEVFREQ is not set
# CONFIG_SYNAPTICS_DMABUF is not set
# CONFIG_SYNAPTICS_IRQCHIP is not set
# CONFIG_SYNAPTICS_INPUT is not set
# CONFIG_SYNAPTICS_BLUETOOTH is not set
# CONFIG_SYNAPTICS_CLOCKSOURCE is not set
# CONFIG_SYNAPTICS_DMA is not set
# CONFIG_SYNAPTICS_TTY is not set
# CONFIG_SYNAPTICS_LEDS is not set
# CONFIG_SYNAPTICS_MFD is not set
# CONFIG_SYNAPTICS_MISC is not set
# CONFIG_SYNAPTICS_MTD is not set
# CONFIG_SYNAPTICS_PWM is not set
# CONFIG_SYNAPTICS_RTC is not set
# CONFIG_SYNAPTICS_SPI is not set
# CONFIG_SYNAPTICS_STAGING is not set
# CONFIG_SYNAPTICS_WATCHDOG is not set
# CONFIG_SYNAPTICS_MAILBOX is not set
# CONFIG_SYNAPTICS_RPMSG is not set
# CONFIG_SYNAPTICS_CRYPTO is not set
CONFIG_UEVENT_HELPER=y
CONFIG_DEVTMPFS=y
CONFIG_DEVTMPFS_MOUNT=y
# CONFIG_ALLOW_DEV_COREDUMP is not set
CONFIG_INPUT_EVDEV=y
# CONFIG_INPUT_KEYBOARD is not set
# CONFIG_INPUT_MOUSE is not set
# CONFIG_SERIO is not set
# CONFIG_VT is not set
# CONFIG_LEGACY_PTYS is not set
# CONFIG_LEGACY_TIOCSTI is not set
CONFIG_SERIAL_8250=y
# CONFIG_SERIAL_8250_DEPRECATED_OPTIONS is not set
CONFIG_SERIAL_8250_CONSOLE=y
CONFIG_SERIAL_8250_NR_UARTS=2
CONFIG_SERIAL_8250_RUNTIME_UARTS=2
CONFIG_SERIAL_8250_DW=y
# CONFIG_HW_RANDOM is not set
# CONFIG_DEVPORT is not set
CONFIG_I2C=y
CONFIG_I2C_CHARDEV=y
CONFIG_I2C_DESIGNWARE_CORE=y
CONFIG_GPIO_SYSFS=y
CONFIG_GPIO_DWAPB=y
CONFIG_GPIO_FXL6408=y
# CONFIG_HWMON is not set
CONFIG_MFD_SYSCON=y
CONFIG_REGULATOR=y
CONFIG_REGULATOR_FIXED_VOLTAGE=y
CONFIG_REGULATOR_GPIO=y
CONFIG_REGULATOR_TPS6286X=y
# CONFIG_HID_SUPPORT is not set
# CONFIG_USB_SUPPORT is not set
CONFIG_DMABUF_HEAPS=y
CONFIG_DMABUF_SYSFS_STATS=y
CONFIG_DMABUF_HEAPS_CMA=y
# CONFIG_VIRTIO_MENU is not set
# CONFIG_VHOST_MENU is not set
# CONFIG_SURFACE_PLATFORMS is not set
# CONFIG_ARM64_PLATFORM_DEVICES is not set
# CONFIG_ARM_ARCH_TIMER_EVTSTREAM is not set
# CONFIG_FSL_ERRATUM_A008585 is not set
# CONFIG_HISILICON_ERRATUM_161010101 is not set
# CONFIG_ARM64_ERRATUM_858921 is not set
# CONFIG_IOMMU_SUPPORT is not set
CONFIG_RESET_CONTROLLER=y
# CONFIG_DNOTIFY is not set
# CONFIG_PROC_PAGE_MONITOR is not set
CONFIG_TMPFS=y
CONFIG_CONFIGFS_FS=y
# CONFIG_MISC_FILESYSTEMS is not set
CONFIG_DMA_CMA=y
CONFIG_PRINTK_TIME=y
# CONFIG_SECTION_MISMATCH_WARN_ONLY is not set
CONFIG_DEBUG_FS=y
# CONFIG_SLUB_DEBUG is not set
CONFIG_SOFTLOCKUP_DETECTOR=y
CONFIG_DEBUG_ATOMIC_SLEEP=y
CONFIG_STACKTRACE=y
# CONFIG_RCU_TRACE is not set
# CONFIG_FTRACE is not set
# CONFIG_STRICT_DEVMEM is not set
# CONFIG_RUNTIME_TESTING_MENU is not set
> 
> For seccomp, the results indicate a benefit (2.98%) from the change.
> 
> Hope this is helpful for maintainers to judge the change.
> 
> I'd leave maintainers to review the code.
> 
> Thanks,
> Leo