Linux Kernel: Add support for using a MAX3421E chip as a host driver

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This change "Add support for using a MAX3421E chip as a host driver." (commit 2d53139) in Linux kernel is authored by David Mosberger <davidm [at] egauge.net> on Mon Apr 28 22:14:07 2014 -0600. Description of "Add support for using a MAX3421E chip as a host driver." The change "Add support for using a MAX3421E chip
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Linux Kernel: cifs: release auth_key.response for reconnect

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This change "cifs: release auth_key.response for reconnect." (commit f5c4ba8) in Linux kernel is authored by Shu Wang <shuwang [at] redhat.com> on Fri Sep 8 18:48:33 2017 +0800. Description of "cifs: release auth_key.response for reconnect." The change "cifs: release auth_key.response for reconnect." introduces changes as follows. cifs: release auth_key.response for reconnect. There is a race that
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Linux Kernel 4.19.70 Release

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This post summarizes new features, bugfixes and changes in Linux kernel release 4.19.70. Linux 4.19.70 Release contains 95 changes, patches or new features. In total, there are 101,521 lines of Linux source code changed/added in Linux 4.19.70 release compared to Linux 4.19 release. To view the source code of Linux 4.19.70 kernel release online, please
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How to get vCPU thread ID in QEMU/KVM host OS?

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In order to collect more information about CPU information internal guest OS, we usually need to get vCPU’s thread ID in host OS. Solution 1: Under directory ‘/sys/fs/cgroup/cpuset/machine’, you will find virtual_machine_name.libvirt-qemu directory. And under this directory, you will find all vCPU sub-directories and under these dirs, you will find vCPU thread IDs. For example
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How to get processes’ I/O utilization percentage

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Two notices: 1, a process has only one main thread which is itself. 2, a process has many threads. Solution 1: Please use taskstats [1] related interfaces, and send TASKSTATS_TYPE_PID and TASKSTATS_TYPE_TGID commands to kernel to get a process’s ‘blkio_delay_total’ parameter for a process with one main thread and a process with threads separately. Solution
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How to set process with lowest priority?

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In system, sometimes, we need backstage threads with very very low priority since it cannot preempt any normal process asks for CPU. SCHED_IDLE class satisfies this requirement which has the priority lower than “nice=19” of CFS. Following code does this. 241 void set_idle_priority(void) { 242 struct sched_param param; 243 param.sched_priority = 0; 244 int s
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Is cin much slower than scanf in C++?

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I frequently hear that cin is significantly slower than scanf in C++. Is this true? And how to improve the efficiency of cin? It is really nice to use most of time. One discussion about that cin is very slow is here: http://apps.topcoder.com/forums/?module=Thread&threadID=508058&start=0&mc=7 In short: cin is not always slower (can be faster actually, see
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Disable WordPress Built-in Canonical URL link tag in HTML head

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The built-in canonical URL function since WordPress 2.9 is great. But under some situation, it is not needed. For example, all the Mingle Forum threads’ canonical URL is set to the URL of the page that contains the [mingleforum] shortcode, which, of course, is wrong. How to diabled it? We can disabled WordPress’s Built-in Canonical
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How To Debug Linux Kernel With Less Efforts

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Introduction In general, if we want to debug Linux Kernel, there are lots of tools such as Linux Perf, Kprobe, BCC, Ktap, etc, and we can also write kernel modules, proc subsystems or system calls for some specific debugging aims. However, if we have to instrument kernel to achieve our goals, usually we would not
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x-data-plane feature in QEMU/KVM

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Abstract In systems, sometimes, we use one global lock to keep synchronization among different threads. This principle also happens in QEMU/KVM (http://wiki.qemu.org/Main_Page) system. However, this may cause lock contention problem. The performance/scalability of whole system will be decreased. In order to solve this problem in QEMU/KVM, x-data-plane feature is designed/implemented, which the high-level idea is
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How sched_min_granularity_ns, sched_latency_ns and sched_wakeup_granularity_ns in CFS affect the timeslice of processes

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Abstract Currently, the most famous process scheduling algorithm in Linux Kernel is Completely Fair Scheduling (CFS) algorithm. The core idea of CFS is to let each process share the same proportional CPU resources to run so that it is fair to each process. In this article, I will introduce how sched_min_granularity_ns and sched_latency_ns work internal
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How migration thread works inside of Linux Kernel

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Abstract In computer systems, resources have to be balanced so that the performance will be better based on the same hardware. In Linux Kernel system, we will see some migration kernel threads running as daemons to do this kind of jobs as follows. In this article, we will discuss how Linux Kernel balances its hardware/software
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How sched_setaffinity works inside of Linux Kernel

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Abstract Sometimes, we may want to migrate one process/thread to one specific CPU for some specific purpose. In the Unix/Linux systems, you may choose sched_setaffinity to finish this job. This article will help you to understand how sched_setaffinity (or other APIs like pthread_setaffinity_np in user-space) works internal Linux kernel. Details SYSCALL_DEFINE3(sched_setaffinity, pid_t, pid, unsigned int,
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How to Measure Time Accurately in Programs

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It is quite common to measure the time in programs using APIs like clock() and gettimeofday(). We may also want to measure the time "accurately" for certain purposes, such as measuring a small piece of code’s execution time for performance analysis, or measuring the time in time-sensitive game software. It is hard to measure the
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Compiling 2.6.29 Kernel Module for VMware Workstation 6.5.2 or VMware Player 2.5.2

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为VMware Workstation 6.5.2 or VMware Player 2.5.2编译2.6.29内核模块 安装好Fedora 11后安装VMware Player 2.5.2时编译内核模块失败。查找了下相关资料,找到如下内容和解决方法。 可能的原因: “The only significant change in fedora 11 comes from gcc, which is more strict about undefined macros, and that sometimes causes vm_check_build to fail.” http://communities.vmware.com/thread/202653 解决方法: 使用一个patch: http://communities.vmware.com/thread/203231