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In the current interrupt reporting mode, each CQ entry reports an interrupt. However, when there are a large number of I/O hardware completion interrupts, the following issue may occur: [ 4682.678657][ C129] irq 134: nobody cared (try booting with the "irqpoll" option) [ 4682.708455][ C129] Call trace: [ 4682.711589][ C129] dump_backtrace+0x0/0x1e4 [ 4682.715934][ C129] show_stack+0x20/0x2c [ 4682.719933][ C129] dump_stack+0xd8/0x140 [ 4682.724017][ C129] __report_bad_irq+0x54/0x180 [ 4682.728625][ C129] note_interrupt+0x1ec/0x2f0 [ 4682.733143][ C129] handle_irq_event+0x118/0x1ac [ 4682.737834][ C129] handle_fasteoi_irq+0xc8/0x200 [ 4682.742613][ C129] __handle_domain_irq+0x84/0xf0 [ 4682.747391][ C129] gic_handle_irq+0x88/0x2c0 [ 4682.751822][ C129] el1_irq+0xbc/0x140 [ 4682.755648][ C129] _find_next_bit.constprop.0+0x20/0x94 [ 4682.761036][ C129] cpumask_next+0x24/0x30 [ 4682.765208][ C129] gic_ipi_send_mask+0x48/0x170 [ 4682.769900][ C129] __ipi_send_mask+0x34/0x110 [ 4682.775720][ C129] smp_cross_call+0x3c/0xcc [ 4682.780064][ C129] arch_send_call_function_single_ipi+0x38/0x44 [ 4682.786146][ C129] send_call_function_single_ipi+0xd0/0xe0 [ 4682.791794][ C129] generic_exec_single+0xb4/0x170 [ 4682.796659][ C129] smp_call_function_single_async+0x2c/0x40 [ 4682.802395][ C129] blk_mq_complete_request_remote.part.0+0xec/0x100 [ 4682.808822][ C129] blk_mq_complete_request+0x30/0x70 [ 4682.813950][ C129] scsi_mq_done+0x48/0xac [ 4682.818128][ C129] sas_scsi_task_done+0xb0/0x150 [libsas] [ 4682.823692][ C129] slot_complete_v3_hw+0x230/0x710 [hisi_sas_v3_hw] [ 4682.830120][ C129] cq_thread_v3_hw+0xbc/0x190 [hisi_sas_v3_hw] [ 4682.836114][ C129] irq_thread_fn+0x34/0xa4 [ 4682.840371][ C129] irq_thread+0xc4/0x130 [ 4682.844455][ C129] kthread+0x108/0x13c [ 4682.848365][ C129] ret_from_fork+0x10/0x18 [ 4682.852621][ C129] handlers: [ 4682.855577][ C129] [<00000000949e52bf>] cq_interrupt_v3_hw [hisi_sas_v3_hw] threaded [<000000005d8e3b68>] cq_thread_v3_hw [hisi_sas_v3_hw] [ 4682.868084][ C129] Disabling IRQ #134 When the IRQ management layer processes each hardware interrupt, if the return value of the interrupt handler is IRQ_WAKE_THREAD, it will wake up the handler thread for this interrupt action and set IRQTF_RUNTHREAD flag, wait for the interrupt handling thread to clear the IRQTF_RUNTHREAD flag after execution. Later in note_interrupt(), use irq_count to count hardware interrupts and irqs_unhandled to count interrupts for which no thread handler is responsible. When irq_count reaches 100000 and irqs_unhandled reaches 99000, irq will be disabled. In the performance test scenario, I/O completion hardware interrupts are continuously and quickly generated. As a result, the interrupt processing thread is cyclically called in irq_thread() and does not exit, this affects the response of the interrupt thread to the hardware interrupt and causes irqs_unhandled to grow to 99000. Finally, the irq is disabled. Therefore, default enable interrupt coalescing to reduce the generation of hardware interrupts, this helps interrupt processing threads to stop calling in irq_thread(). For interrupt coalescing, according to the actual performance test, set the count of CQ entries to 10 and the interrupt coalescing timeout period to 10us based on the actual performance test. Before and after interrupt coalescing is enabled, the 4K read/write performance is improved by about 3%, and the 256K read/write performance is basically the same. Signed-off-by: Yihang Li <liyihang9@huawei.com> Link: https://lore.kernel.org/r/20241008021822.2617339-9-liyihang9@huawei.com Reviewed-by: Xiang Chen <chenxiang66@hisilicon.com> Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.