Linux 上 Intel CPU 的安全性修正與效能的影響

Hacker News Daily 上看到在講 Intel CPU 因為各種安全性問題,而需要在 Linux Kernel 上修正,所產生的效能問題:「HOWTO make Linux run blazing fast (again) on Intel CPUs」。

這一系列的子彈也飛得夠久了 (雖然還是一直有其他的小子彈在飛),所以回過頭來看一下目前的情況。

這邊主要的測試是針對 mitigations=off 與 SMT 的啟用兩個項目在測 (SMT 在 Intel 上叫做 Hyper-threading),可以看到這兩份測試結果,目前的 mitigation 對效能的影響其實已經逐漸降到可以接受的程度 (小於 5%),但關閉 SMT 造成的效能影響大約都在 20%~30%:

但是開啟 SMT 基本上是個大坑,如果有關注大家在挖洞的對象,可以看到一堆 Intel CPU 上專屬的安全性問題都跟 SMT 有關...

剛好岔個題聊一下,先前弄了一顆 AMDRyzen 7 3700X 在用 (也是跑 Linux 桌機),才感受到現在的網頁真的很吃 CPU,開個網頁版的 SlackOffice 365 的速度比原來的老機器快了好多,差點想要把家裡的桌機也換掉...

Google Chrome 對 CPU bug 的 patch

既然有方向了,後續應該會有人去找底層的問題...

先是在 Hacker News 上看到「Speculative fix to crashes from a CPU bug」這個猜測性的修正,這是因為他們發現在 IntelGemini Lake 低功耗晶片組上會發生很詭異的 crash:

For the last few months Chrome has been seeing many "impossible" crashes on Intel Gemini Lake, family 6 model 122 stepping 1 CPUs. These crashes only happen with 64-bit Chrome and only happen in the prologue of two functions. The crashes come and go across different Chrome versions.

然後依照 crash log 猜測跟 alignment 有關,所以決定用 gcc/clang 都有支援的 __attribute__ 強制設定 alignment 來避開,但看起來手上沒有可以重製的環境,所以只能先把實做丟上來...

EC2 要從 Instance 數量限制改成 vCPU 數量限制

這算是 AWS 的保護機制,在 Amazon EC2 上能開的機器數量都是有限制的。

打算要用新的 vCPU 數量限制取代舊的 Instance 數量限制:「Using new vCPU-based On-Demand Instance limits with Amazon EC2」,然後現在可以先加入:「vCPU-based On-Demand Instance Limits are Now Available in Amazon EC2」。

這次改善的問題是,以往 m5.largem5.xlarge 是兩個不同的限制,所以用起來會比較卡,現在則改成用 vCPU 來管理。

這次的架構是改成,一般性的機器會有一個 vCPU 數量限制,其他不同特性的各自有自己的 vCPU 數量限制:

In addition to now measuring usage in number of vCPUs, there will only be five different On-Demand Instance limits—one limit that governs the usage of standard instance families such as A, C, D, H, I, M, R, T, and Z, and one limit per accelerated instance family for FPGA (F), graphic-intensive (G), general purpose GPU (P), and special memory optimized (X) instances.

9/24 可以先手動加入,會拿你現在的量會換算過去,然後 10/24 會全部都轉過去:

During a transition period from September 24, 2019, through October 24, 2019, you can opt in to receive vCPU-based instance limits. When you opt in, EC2 automatically computes your new limits, giving you access to launch at least the same number of instances (if not more) than you do currently. Beginning October 24, 2019, all accounts will switch to vCPU-based instance limits, and the current count-based instance limits will no longer be supported. Although the switchover will not impact your ability to launch EC2 instances, you should familiarize yourself with the new On-Demand Instance limits experience and opt into vCPU limits at a time of your choosing.

應該是會方便一些...

IBM 把 OpenPOWER Foundation 交給 The Linux Foundation

標題雖然是「Big Blue Open Sources Power Chip Instruction Set」,但實質上應該就是 IBMOpenPOWER Foundation 交給 The Linux Foundation

找了一下兩邊的新聞稿,其中 The Linux Foundation 的新聞稿在「The Linux Foundation Announces New Open Hardware Technologies and Collaboration」這邊,但 OpenPOWER 的網站好像從 2018 年年底就沒更新了...

開放硬體最近比較紅的應該是 RISC-VOpenRISC 這些專案?IBM 這一招不知道是怎麼樣...

重新了解 Amazon EC2 的 T2/T3 Unlimited

剛好跟同事聊到 Amazon EC2 的 T2/T3 Unlimited,因為有些疑惑所以回家查了一下資料,發現以前的理解不夠完整。這是 T2/T3 Unlimited 的說明文件:「Unlimited Mode for Burstable Performance Instances」。

在文件的這塊說明了 T2/T3 Unlimited 模式的計算方式:

When its CPU utilization falls below the baseline, it uses the CPU credits that it earns to pay down the surplus credits that it spent earlier. The ability to earn CPU credits to pay down surplus credits enables Amazon EC2 to average the CPU utilization of an instance over a 24-hour period. If the average CPU usage over a 24-hour period exceeds the baseline, the instance is billed for the additional usage at a flat additional rate per vCPU-hour.

我本來以為是剩下的 CPU credit 不夠時就會被收費,但依照官方文件的說明,是可以用後面賺到的 CPU credit 支付前面使用的 CPU credit,而可跨越的時間區間是 24 小時。

所以有時候會在 AWS web console 上看到 CPU 沒有在用,但是 CPU credit 卻長回不來的情況,是因為這時候還在還之前的債...

用 Machine Learning 改善 Streaming 品質的服務與論文

Hacker News 上看到「Puffer」這個服務,裡面利用了 machine learning algorithm 動態調整 bitrate,以提昇傳輸品質。

測試得到的數據後來被整理起來一起放進論文:「Continual learning improves Internet video streaming」。

在開頭介紹了 Fugu 這個演算法:

We describe Fugu, a continual learning algorithm for bitrate selection in streaming video.

而 Puffer 就是實驗網站:

We evaluate Fugu with Puffer, a public website we built that streams live TV using Fugu and existing algorithms. Over a nine-day period in January 2019, Puffer streamed 8,131 hours of video to 3,719 unique users.

這個站台提供了許多真實的頻道進行測試:

Stream live TV in your browser. There's no charge. You can watch U.S. TV stations affiliated with the NBC, CBS, ABC, PBS, FOX, and Univision networks.

可以看到 Fugu 的結果很好,比起其他提出的方案是全面性的改善:

這邊是用 WebSocket 測試,並且配合了不同的 TCP congestion algorithm,沒有太考慮額外的計算成本...

Ubuntu 改變放掉 i386 的計畫

先前在「Ubuntu 19.10 要放掉 i386 架構」這邊提到 Ubuntu 要放掉 i386 的計畫,因為造成的迴響很大,現在官方決定修改本來的結論:「Statement on 32-bit i386 packages for Ubuntu 19.10 and 20.04 LTS」。

在本來的計畫裡,是完全放生 i386 架構 (完全不管):

While this means we will not provide 32-bit builds of new upstream versions of libraries, there are a number of ways that 32-bit applications can continue to be made available to users of later Ubuntu releases, as detailed in [4]. We will be working to polish the 32-bit support story over the course of the 19.10 development cycle. To follow the evolution of this support, you can participate in the discourse thread at [5].

現在則是打算透過 container 技術支援 32-bit library & binary,算是某種緩衝方式:

We will also work with the WINE, Ubuntu Studio and gaming communities to use container technology to address the ultimate end of life of 32-bit libraries; it should stay possible to run old applications on newer versions of Ubuntu. Snaps and LXD enable us both to have complete 32-bit environments, and bundled libraries, to solve these issues in the long term.

但應該還是會有程式沒辦法在 container 環境裡跑,看起來官方決定放掉了...

Raspberry Pi 4 開賣,USD$35

Raspberry Pi 4 開賣,目前推出的是 Model B,最低規格的 1GB RAM 版本與之前 RPi 3 相同都是 USD$35,另外這次提供了以前沒有的 2GB 與 4GB 版本,分別是 USD$45 與 USD$55:「Raspberry Pi 4 on sale now from $35」。

有兩個比較大而且要注意的改變,第一個是電源接頭變成 Type-C 了:

We’ve moved from USB micro-B to USB-C for our power connector. This supports an extra 500mA of current, ensuring we have a full 1.2A for downstream USB devices, even under heavy CPU load.

另外一個是 HDMI 接頭換成 D Type:

To accommodate dual display output within the existing board footprint, we’ve replaced the type-A (full-size) HDMI connector with a pair of type-D (micro) HDMI connectors.

這兩個改變都需要準備額外的設備或是線材,其他的改變應該還好...

這次改版最明顯的是效能的增加,官方宣稱 CPU 速度是前一代的三倍:

A 1.5GHz quad-core 64-bit ARM Cortex-A72 CPU (~3× performance)

而在 GPU 相關的則是對 H.265 的 4Kp60 硬體解壓縮:

4Kp60 hardware decode of HEVC video

先前用 RPi 3 放客廳還是覺得不太夠,也許可以考慮看看這個...

EC2 的 C5 系列機器推出 12x、24x 以及 metal 類別

EC2c5 系列主機推出了 12xlarge24xlarge 以及 metal 三種新的類別:「Now Available: New C5 instance sizes and bare metal instances」。

本來的 c5largexlarge2xlarge4xlarge9xlarge (這邊有一些不規則了),現在多了 12xlarge24xlarge,應該是大到需要依照硬體規格對齊數字了?

另外一個是,c5.24xlargec5.metal 其實是一樣的硬體規格 (以及價錢),主要的差異在 c5.metal 沒有虛擬化,所以除了壓榨效能以外,還可以看到很多硬體資訊:

  • do not want to take the performance hit of nested virtualization,
  • need access to physical resources and low-level hardware features, such as performance counters and Intel VT that are not always available or fully supported in virtualized environments,
  • are intended to run directly on the hardware, or licensed and supported for use in non-virtualized environments.

Ubuntu 19.10 要放掉 i386 架構

Ubuntu 19.10 版將不再支援 i386 架構了:「i386 architecture will be dropped starting with eoan (Ubuntu 19.10)」。

查了一下 x86-64 條目,AMD 的第一個 x86-64 版本是在 2003 年四月推出的:

The first AMD64-based processor, the Opteron, was released in April 2003.

Intel 則是在 2004 年六月推出:

The first processor to implement Intel 64 was the multi-socket processor Xeon code-named Nocona in June 2004.

但是 mobile 版的是 2006 年七月:

The first Intel mobile processor implementing Intel 64 is the Merom version of the Core 2 processor, which was released on July 27, 2006.

不論如何都已經十年了,如果考慮到 Ubuntu 18.04 提供五年支援,其實到 2023 年四月前都還有得用...