Terminal

Generally speaking a terminal is a relatively dumb electromechanical device with an input interface (like a keyboard) and an output interface (like a display or sheet of paper).

The computer has an UART driver to read for the hardware device. The sequence of characters is passed to TTY driver which applies the line discipline. The line discipline is in charge of converting special characters (like end of line, backspaces), and echoing what has been received back to the teletype, so that the user can see what it has been typed (line disciplines will be discussed in the next post of the series).

The words terminal and TTY device are basically interchangeable as they mean the same thing.

Introduction

Signals are software interrupts sent to a program to indicate that an important event has occurred. The events can vary from user requests to illegal memory access errors. Some signals, such as the interrupt signal, indicate that a user has asked the program to do something that is not in the usual flow of control.

Every signal has a default action associated with it. The default action for a signal is the action that a script or program performs when it receives a signal.
Some of the possible default actions are

• Terminate the process.
• Ignore the signal.
• Dump core. This creates a file called core containing the memory image of the process when it received the signal.
• Stop the process.(can run later on)
• Continue a stopped process

Introduction

WebSocket is a protocol providing full-duplex communication channels over a single TCP connection. The WebSocket protocol was standardized by the IETF as RFC 6455 in 2011, and the WebSocket API in Web IDL is being standardized by the W3C.

WebSocket is designed to be implemented in web browsers and web servers, but it can be used by any client or server application. The WebSocket Protocol is an independent TCP-based protocol. Its only relationship to HTTP is that its handshake is interpreted by HTTP servers as an Upgrade request. The WebSocket protocol makes more interaction between a browser and a web server possible, facilitating the real-time data transfer from and to the server. This is made possible by providing a standardized way for the server to send content to the browser without being solicited by the client, and allowing for messages to be passed back and forth while keeping the connection open. In this way, a two-way (bi-directional) ongoing conversation can take place between a browser and the server. The communications are done over TCP port number 80, which is of benefit for those environments which block non-web Internet connections using a firewall. Similar two-way browser-server communications have been achieved in non-standardized ways using stopgap technologies such as Comet.

grpc

In gRPC, a client application can directly call a method on a server application on a different machine as if it were a local object, making it easier for you to create distributed applications and services. As in many RPC systems, gRPC is based around the idea of defining a service, specifying the methods that can be called remotely with their parameters and return types. On the server side, the server implements this interface and runs a gRPC server to handle client calls. On the client side, the client has a stub (referred to as just a client in some languages) that provides the same methods as the server.

Overview

Libvirt is collection of software that provides a convenient way to manage virtual machines and other virtualization functionality, such as storage and network interface management. These software pieces include an API library, a daemon (libvirtd), and a command line utility (virsh).

An primary goal of libvirt is to provide a single way to manage multiple different virtualization providers/hypervisors.

The libvirt project:

• is a toolkit to manage virtualization platforms
• is accessible from C, Python, Perl, Go and more
• is licensed under open source licenses
• supports KVM, QEMU, Xen, Virtuozzo, VMWare ESX, LXC, and more
• targets Linux, FreeBSD, Windows and macOS

Overview

When talking about virtio-networking we can separate the discussion into two layers:

• Control plane - Used for capability exchange negotiation between the host and guest both for establishing and terminating the data plane.
• Data plane - Used for transferring the actual data (packets) between host and guest.

It’s important to distinguish between these layers since they have different requirements (such as performance) and different implementations

Fundamentally the data plane is required to be as efficient as possible for moving the packets fast while the control plane is required to be as flexible as possible for supporting different devices and vendors in future architectures.

Introduction

Virtual machine uses host device by three different types.

• Full Emulated devices
• Paravirtualized devices
• Physically shared devices

As the first way has low performance for IO intensive VM, hence it should not be used in cloud provider, so let’s focus on the later two.
Paravirtualization provides a fast and efficient means of communication for guests to use devices on the host machine, The popular one is virtio.

Physically shared devices(Direct/IO, Passthrough) is more efficient than Paravirtualization for IO intensive VM, but it needs hardware IOMMU support.

FAQ

How to enable EPT

EPT is feature of CPU, but there is no independent switch for EPT feature, to turn it on or off, that means if you CPU supports it, it's turned on or off along with VT-X from BIOS
check EPT supported or not

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 lscpu | grep ept
Flags:                 fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf eagerfpu pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 fma cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm abm 3dnowprefetch epb cat_l3 cdp_l3 intel_pt tpr_shadow vnmi flexpriority ept vpid fsgsbase tsc_adjust bmi1 hle avx2 smep bmi2 erms invpcid rtm cqm rdt_a rdseed adx smap xsaveopt cqm_llc cqm_occup_llc cqm_mbm_total cqm_mbm_local dtherm ida arat pln pts

FAQ

Intel vt-x vs vt-d

VT-x is CPU virtualization technology from intel, while VT-d is IO virtualization technology from intel as well.

• VT-x which supports root mode and vmx mode for cpu and series of instructions for use to support cpu virtualization.
• VT-d(Intel® Virtualization Technology for Directed I/O) is technology which supports IOMMU, hence can provide Direct/IO, IO passthrough to guest VM.

How to enable vt-x and vt-d

If you CPU supports these, there is a switch in BIOS to enable/disable them, the switch is mostly located at Processor tab.

check VT-x enabled or not

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# vmx Virtual Machine Extensions
$ lscpu | grep vmx
Flags:                 fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf eagerfpu pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 fma cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm abm 3dnowprefetch epb cat_l3 cdp_l3 intel_pt tpr_shadow vnmi flexpriority ept vpid fsgsbase tsc_adjust bmi1 hle avx2 smep bmi2 erms invpcid rtm cqm rdt_a rdseed adx smap xsaveopt cqm_llc cqm_occup_llc cqm_mbm_total cqm_mbm_local dtherm ida arat pln pts

check VT-d enabled or not
When vt-d is enable and IOMMU kernel is loaded, at system boot time, IOMMU is initialized

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# centos7
$ dmesg | grep "DMAR:"
[    0.000000] DMAR: IOMMU enabled
...

Introduction

Virtual GPU (vGPU) enables multiple virtual machines (VMs) to have simultaneous, direct access to a single physical GPU, using the same graphics drivers that are deployed on non-virtualized operating systems. By doing this, vGPU provides VMs with unparalleled graphics performance, compute performance, and application compatibility, together with the cost-effectiveness and scalability brought about by sharing a GPU among multiple workloads.