Tag: l2

Linode 的 VPC 與 VLAN

看到 Linode 的「Go Private with VLANs and VPCs」這篇，裡面特地提到了 VLAN：

Can a VLAN be used as a VPC on Linode?

The short answer is again, yes, we can use a VLAN as a VPC on Linode.

在「Common Use Cases for Linode's VLAN Service」這篇 (發現是 2021 年就有的資料) 裡面開頭就有提到：

This means that two or more Linodes connected via the VLAN can see each other as if they were directly connected to the same physical Ethernet network. This network supports all the logical Ethernet features like L2 broadcast and L2 multicast.

所以看起來的確是在 Linode 的 SDN 上面支援了 VLAN。記得早期是用 Cisco 的方案 (2013 年的時候有「Linode NextGen: The Network」這篇)，現在不知道是什麼架構...

Working Set Size (WSS) 的想法

Netflix 的 Brendan Gregg (他比較知名的發明是 Flame Graph) 寫了一篇「How To Measure the Working Set Size on Linux」，他想要量測單位時間內會用到的記憶體區塊大小：

The Working Set Size (WSS) is how much memory an application needs to keep working. Your app may have populated 100 Gbytes of main memory, but only uses 50 Mbytes each second to do its job. That's the working set size. It is used for capacity planning and scalability analysis.

這可以拿來分析這些應用程式是否能夠利用 L1/L2/L3 cache 大幅增加執行速度，於是就可以做成圖，像是這樣：

在 Netflix 這樣人數的公司，需要設計一些有用的指標，另外發展出對應的工具，讓其他人更容易迅速掌握狀況，畢竟不是每個人都有上天下海的能力，遇到狀況可以馬上有頭緒進行 trouble shooting...