Weiwei Jia

Weiwei Jia is a Ph.D. student in the Department of Computer Science at New Jersey Institute of Technology since 2016. His research interests are include storage systems, operating systems and computer systems.

How To Debug Linux Kernel With Less Efforts

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 like to pay more efforts like above solutions since we’d like to achieve our aims quickly and easily. » Read more

QEMU/KVM Network Mechanisms

Introduction As we know, network subsystems are important in computer systems since they are I/O systems and need to be optimized with many algorithms and skills. This article will introduce how QEMU/KVM [2] network part works. In order to put everything simple and easy to understand, we will begin with several examples and then understand how it works internally. Examples In this example, we will use TAP device [1] as QEMU/KVM host network device driver and VirtIO driver will be used to send/receive network packets/data between Host OS and Guest OS. » Read more

I/O Microscopy: Tasks’ Disk I/O Information with High Accuracy

Abstract Most popular task monitor systems (such as top, iotop, proc, etc) can only get tasks’ disk I/O information like tasks’ I/O utilization percentage every seconds due to kernel timer/tick frequency and high time cost of system interfaces. This article presents I/O Microscopy, a new way to get tasks’ disk I/O information with high accuracy. Experiments show that I/O microscopy can filter out I/O intensive tasks effectively. » Read more

How does linux kernel collect task stats data

Motivation ∞ Recently, I find it is hard to know the percentage of time that one process uses to wait for synchronous I/O (eg, read, etc). One way is to use the taskstats API provided by Linux Kernel [1]. However, for this way, the precision may be one problem. With this problem, I dig into Linux Kernel source codes to see how “blkio_delay_total” (Delay time waiting for synchronous block I/O to complete) is calculated. » Read more

x-data-plane feature in QEMU/KVM

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 “I/O requests are handled by dedicated IOThread rather than QEMU main loop threads so that it will not have lock contention among I/O threads and other QEMU main loop threads”. » Read more

The length of timeslices for processes under CFS process scheduling algorithm in Linux Kernel

Abstract As is known, CFS (Completely Fair Scheduling) is a famous process scheduling algorithm in Linux Kernel but there is no convenient way for developers to get the timeslices of processes if CFS is chosen. In this article, I will introduce one way to hack the timeslices of process easily for CFS in Linux Kernel. Note that, the way introduced following is under Linux Kernel 3.16.39. » Read more

How sched_min_granularity_ns, sched_latency_ns and sched_wakeup_granularity_ns in CFS affect the timeslice of processes

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 CFS to affect the timeslice of processes. » Read more

How migration thread works inside of Linux Kernel

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 resources (NOTE: this article is based on Linux Kernel 4.7 and other versions may have some differences). » Read more

How sched_setaffinity works inside of Linux Kernel

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 -- sched_setaffinity(pid_t pid, const struct cpumask *in_mask) --- __set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask, bool check) ---- stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg) ----- migration_cpu_stop(void *data) ------ __migrate_task(struct rq *rq, struct task_struct *p, int dest_cpu) ------- move_queued_task(struct rq *rq, struct task_struct *p, int new_cpu) -------- enqueue_task(struct rq *rq, struct task_struct *p, int flags) --------- returns the new run queue of destination CPU Above character steps give a workflow of how sched_setaffinity works (how it migrates one process/thread from the run queue of source CPU to the run queue of destination CPU). » Read more

Infrastructure Software For Fedora

Fedora is a popular distro supported by the RedHat Corporation. This article recommends you some infrastructure software and how to install them in details. Minimize and Maximize window ∞ 1, Install software gnome-tweak-tool # yum install gnome-tweak-tool 2, Start gnome-tweak-tool and set minimizing and maximizing functions as follows. 1.png 2.png Actually, gnome-tweak-tool has more functions than what I say above. You can install others yourself. » Read more

Connecting to Remote Servers by VNC on Windows

Software you will need 1, Putty 2, Real VNC viewer 3, twm (lightweight desktop). On fedora (centos, redhat): sudo yum install twm (on other distros, you may need other commands, or download source code and install it). Specific steps ∞ 1, Enter your Host name and port in putty. 1_9.jpg 2, Set port forwarding in putty Tunnels. 1_7.jpg 3, Start vncserver in the server side. » Read more