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网址：https://www.kernel.org/doc/html/latest/vm/page_migration.htmlPage migration allows moving the physical location of pages between nodes in a NUMA system while the process is running. This means that the virtual addresses that the process sees do not cha

code path：https://elixir.bootlin.com/linux/v4.9.269/source/include/linux/page-flags.hPAGEFLAG(Active, active, PF_HEAD) __CLEARPAGEFLAG(Active, active, PF_HEAD)TESTCLEARFLAG(Active, active, PF_HEAD)#define PAGEFLAG(uname, lname, policy) \ TESTPAGE

/** * __get_user_pages() - pin user pages in memory * @tsk: task_struct of target task * @mm: mm_struct of target mm * @start: starting user address * @nr_pages: number of pages from start to pin * @gup_flags: flags modifying pin behaviour * @pages

vmap(). This can be used to make a long duration mapping of multiple physical pages into a contiguous virtual space. It needs global synchronization to unmap.kmap(). This permits a short duration mapping of a single page. It needs global synchronization,

1 .lib/dump_stack.cstatic void __dump_stack(void){ dump_stack_print_info(KERN_DEFAULT); show_stack(NULL, NULL);}2 .arch/arm64/kernel/traps.cvoid show_stack(struct task_struct *tsk, unsigned long *sp){ dump_backtrace(NULL, tsk); barrier();}dum

建议使用以下方式进行vb2_queue 进行initstruct vb2_queue *q;q->mem_ops = &vb2_dma_sg_memops;这样 userspace reqbufs 就会使用 vb2_dma_sg_alloc 最终得到的是 struct sg_table *sgt;[ 43.365265]<3>[W](3)[<ffffff800808bb7c>] dump_backtrace+0x0/0x2c0[ 43.366029]

V4L2_MEMORY_MMAP 导出 fd 需要使用 vb2_ioctl_expbuf (只能使用于VB2_MEMORY_MMAP 方式)。int buffer_export(int v4lfd, enum v4l2_buf_type bt, int index, int *dmafd){ struct v4l2_exportbuffer expbuf; memset(&expbuf, 0, sizeof(expbuf)); expbuf.type = bt;

user space struct v4l2_buffer buf; memset(&buf, 0, sizeof buf); buf.index = 0; buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; buf.memory = V4L2_MEMORY_DMABUF; buf.m.fd = dbuf_fd; ret = ioctl(v4lfd, VIDIOC_QBUF, &buf);kernel/** * __qbuf_d

spinlock_t数据类型，spin_lock(&lock)和spin_unlock(&lock)是加锁和解锁等待解锁的进程将反复检查锁是否释放，而不会进入睡眠状态(忙等待)，所以常用于短期保护某段代码同时，持有自旋锁的进程也不允许睡眠，不然会造成死锁——因为睡眠可能造成持有锁的进程被重新调度，而再次申请自己已持有的锁。wait_for_completion，主要调用wait_for_common，而wait_for_common则主要是将当前线程加入等待队列，然后调用schedul

debug 方法1cat /sys/kernel/debug/gpio

[ 6.535890]<3>[I](3)OF: of_irq_parse_one: dev=/soc/xxx@12300000, index=0[ 6.536771]<3>[W](3)CPU: 3 PID: 1 Comm: swapper/0 Not tainted 4.9.118+ #356[ 6.537638]<3>[W](3)Hardware name: ATC Inc. AC8x (DT)[ 6.538266]<3>[W]

What memory is DMA'able?========================The first piece of information you must know is what kernel memory canbe used with the DMA mapping facilities. There has been an unwrittenset of rules regarding this, and this text is an attempt to fin.

dump 寄存器 show_regs(regs);code ： https://elixir.bootlin.com/linux/v4.9.185/source/arch/arm64/kernel/process.cvoid __show_regs(struct pt_regs *regs){int i, top_reg;u64 lr, sp;if (compat_user_mode(regs)) { lr = regs->compat_lr; sp = regs->co.

kernel log 出现 lowmemorykiller 判断 kernel 出现了内存泄漏多次测试后对比 procrank 数据adb shell procrank > C:\procrank.txt测试前：RAM: 1814588K total, 359780K free, 7372K buffers, 701496K cached, 964K shmem, 138804K slab测试后：RAM: 1814588K total, 229016K free, 10204K

1.使用方法userspacestruct v4l2_requestbuffers reqbufs = { .count = 5, .type = V4L2_BUF_TYPE_VIDEO_CAPTURE, .memory = V4L2_MEMORY_MMAP,};ioctl(dev_fd,VIDIOC_REQBUFS,&reqbufs);void *ptr[5];for (int i =0; i < 5 ; i++) { ptr[i] = mmap()NULL,buffe

wait_event_interruptible souece code#define __wait_event_interruptible(wq, condition, ret) \do { \ DEFINE_WAIT(__wait); \ \ for (;;) { \ prepare_to_wait(&wq, &__wait, TASK_INTERRUPTIBLE); \ if (condition)

1.queue buf 过程Qcom HAL code/*=========================================================================== * FUNCTION : mm_stream_qbuf * * DESCRIPTION: enqueue buffer back to kernel queue for fu...

1.buffer地址偏移以分辨率 1280*720 格式为YV12 为例，Y起始地址为0x100000000 ,且是连续y_addr = 0x100000000;cb_addr = y_addr + 1280×720；cr_addr = cb_addr + 1280*720/4;2.line stride计算需要考虑到不同硬件使用相同的地址，如camera 写buffer...

top -H -O CPU 查看线程运行在相应的CPU上···top -H -O CPU[?25lTasks: 907 total, 2 running, 901 sleeping, 0 stopped, 0 zombieMem: 1853188k total, 1307684k used, 54550...

假设定义了一个结构体struct mutex_lock { struct mutex lock; }struct mutex_lock mutex_lock_t;在 mutex_init(&mutex_lock_t.lock)在后面的函数中调用了 memset(&mutex_lock_t,0,sizeof(struct mutex_lock)) ,...

写 android 驱动 的基本功就是把自己driver如何在kernel 中编译，下面将以led驱动为例1.定义使用的deconfig代码路径：kernel/arch/arm64/configs/xxxxx_defconfigCONFIG_XX_YY=y y 编译到内核m 编译成ko文件2.驱动上级目录中的配置代码路径：drivers/soc/Makefileobj-$(...

mmap在linux哪里？什么是mmap？上图说了，mmap是操作这些设备的一种方法，所谓操作设备，比如IO端口（点亮一个LED）、LCD控制器、磁盘控制器，实际上就是往设备的物理地址读写数据。但是，由于应用程序不能直接操作设备硬件地址，所以操作系统提供了这样的一种机制——内存映射，把设备地址映射到进程虚拟地址，mmap就是实现内存映射的接口。操作设备还有很多方法，如ioctl、iore...

ISRs (Interrupt handlers (ISRs))are critical pieces of code that directly converse with the hardware. They are given the privilege of instant execution in the larger interest of system performance. Ho...