On 2024/9/4 16:01, Ming Lei wrote: > On Tue, Sep 03, 2024 at 07:54:37PM +0800, ZhangHui wrote: >> From: zhanghui <zhanghui31@xxxxxxxxxx> >> >> Currently, for a controller that supports multiple queues, like UFS4.0, >> the mq_ops->complete is executed in the interrupt top-half. Therefore, >> the file system's end io is executed during the request completion process, >> such as f2fs_write_end_io on smartphone. >> >> However, we found that the execution time of the file system end io >> is strongly related to the size of the bio and the processing speed >> of the CPU. Because the file system's end io will traverse every page >> in bio, this is a very time-consuming operation. >> >> We measured that the 80M bio write operation on the little CPU will > What is 80M bio? > > It is one known issue that soft lockup may be triggered in case of N:M > blk-mq mapping, but not sure if that is the case. > > What is nr_hw_queues(blk_mq) and nr_cpus in your system? > >> cause the execution time of the top-half to be greater than 100ms. >> The CPU tick on a smartphone is only 4ms, which will undoubtedly affect >> scheduling efficiency. > schedule is off too in softirq(bottom-half). > >> Let's fixed this issue by moved non sync request completion flow to >> softirq, and keep the sync request completion in the top-half. > If you do care interrupt-off or schedule-off latency, you may have to move > the IO handling into thread context in the driver. > > BTW, threaded irq can't help you too. > > > Thanks, > Ming > hi Ming, Very good reminder, thank you. On smartphones, nr_hw_queues and nr_cpus are 1:1, I am more concerned about the interrupt-off latency, which is more obvious on little cores. Moving time-consuming work to the bottom half may not help with schedule latency, but it is may helpful for interrupt response latency of other modules in the system? Thanks Zhang
