幾個其他 Teams 的替代方案 (但還是連到 Teams 伺服器)

這邊講的替代方案不是換掉 Teams,而是找其他的方法連上 Teams 伺服器,畢竟用 Teams 的人大多都沒得選...

在「Teams is killing my Mac every day (microsoft.com)」這邊看到的一些資料可以嘗試,裡面有很多抱怨 Teams 的問題,但還是有些人有給出一些 workaround。

大家主要遇到的問題除了 CPU 吃很兇以外,另外就是記憶體這塊。

一種方法是是用 Edge 瀏覽器的 extension 來跑,我本來想看看 Linux 上的 Brave 能不能裝,但沒有看到對應的安裝連結,大概是 Edge 限定:

If you don't want to use the Microsoft Teams app (which uses a lot of resources), you can:

1. Install the Microsoft Edge Web browser on your Mac

2. Log into https://teams.microsoft.com

3. Click ... > Apps > Install this site as an app

This will create an Edge app for Teams that uses almost no resources but has feature parity with the regular Microsoft Teams app.

We tell all of our students to do this, and it has solved all Microsoft Teams performance issues on student Macs (both Intel and Apple Silicon).

另外有人提到其實官方是有放 M1 的 preview 版本的,雖然不是正式版,但總是比 Intel 版本會好一些:

If you're running an Apple Silicon Mac you can get an early build of Teams osx-arm64 from the exploration build link listed here.[0]

I've been running a daily build for a few weeks and it's noticeably better than the Intel build on an M1 Pro. It launches in half the time and feels far more responsive (probably due to not needing to use the Rosetta JIT for Electron). That said it's still a daily "exploration" build so YMMV.

[0] https://raw.githubusercontent.com/ItzLevvie/MicrosoftTeams-msinternal/master/defconfig

據說會少吃一點點記憶體,就真的大概一點點:

Can confirm it is snappier on a M1 Macbook Pro and using *less* RAM, maybe about 10% less.

但據說這個 preview 版本在自我更新時會跳到 Intel 版本,還要再找一下 workaround 關掉自動更新:

How do you prevent it from automatically updating to the Intel version? I keep downloading the preview builds and they keep getting updated.

後面還有看到有人說他直接實體隔離,把這些肥滋滋的 app 跑在另外一台 Mac 上,然後透過 Universal Control 使用,大多數的情況下都夠用,真的有需要分享畫面時再跑在自己機器上,用完就可以關掉:

Thanks for the tip. I'll give this a try!

For work, I have to run Microsoft Teams, Slack, and Discord. Of those 3, Slack surprisingly uses the least amount of memory (~700 MB), and Teams uses the most (~1.5 GB). I dusted off an old Intel Mac (literally) and interact with it using Universal Control. It only runs those 3 chat apps + mail. It's turned out to be a great way to offload resource hogs and as an added benefit, it minimizes distractions. I'll occasionally glance at the dock to see if there are any notification badges, whereas on my main Mac, I'd feel compelled to deal with notifications immediately.

When I have to share my screen or focus on a conversation, I'll fire up one of those 3 apps on my main (M1) Mac and quit it when I'm done.

Universal Control still feels rough around the edges, but it has saved me from ditching my Macbook Air and shelling out for an M1 Macbook Pro. Sometimes there are issues with reconnecting to the Intel Mac, but it seems to resolve itself if I wait a bit or turn off/on wifi.

大家都在找方法 XDDD

這次 OpenSSL 的兩個 CVE

難得在 Hacker News 首頁上看到 OpenSSLCVE:「OpenSSL Security Advisory [5 July 2022]」,相關的討論在「OpenSSL Security Advisory (openssl.org)」。

第一個 CVE 是 RCE 等級,但觸發條件有點多:

首先是 RSA 2048bits,這個條件應該算容易發生的。

第二個是,因為這個安全問題是因為 OpenSSL 3.0.4 才引入的程式碼,而 OpenSSL 3.0.4 是 2022/06/21 發表的,未必有很多人有升級。

第三個是,因為這次出包的段落是用到了 AVX-512 指令集,一定要 Intel 或是 Centaur 的 CPU,後面這家公司前身就是威盛 (VIA) 的一員,去年賣給了 Intel (然後發現連官網用的 domain 都沒續約...)。

AMD 雖然在 Zen 4 架構上支援 AVX-512,但還沒推出產品,所以直接閃避 XD

另外第三個還有額外的限制,因為這次用到的是 IFMA 指令集,所以也不是所有有支援 AVX-512 的 CPU 都會中獎:

只看 Intel 的部份,第一個支援 IFMA 的是 2018 年推出的 Cannon Lake,這個架構只有一顆行動版的 Intel® Core™ i3-8121U Processor

真正大量支援 IFMA 的是 2019 後的 Intel CPU 了,但到了去年推出的 Alder Lake 因為 E-core 不支援 AVX-512 的關係 (但 P-core 支援),預設又關掉了。

所以如果問這個 bug 嚴不嚴重,當然是很嚴重,但影響範圍就有點微妙了。

接下來講第二個 CVE,是 AES OCB 的實做問題,比較有趣的地方是 Hacker News 上的討論引出了 Mosh 的作者跳出來說明,他居然提到他們在二月的時候試著換到 OpenSSL 的 AES OCB 時有測出這個 bug,被 test case 擋下來了:

Mosh uses AES-OCB (and has since 2011), and we found this bug when we tried to switch over to the OpenSSL implementation (away from our own ocb.cc taken from the original authors) and Launchpad ran it through our CI testsuite as part of the Mosh dev PPA build for i686 Ubuntu. (It wasn't caught by GitHub Actions because it only happens on 32-bit x86.) https://github.com/mobile-shell/mosh/issues/1174 for more.

So I would say (a) OCB is widely used, at least by the ~million Mosh users on various platforms, and (b) this episode somewhat reinforces my (perhaps overweight already) paranoia about depending on other people's code or the blast radius of even well-meaning pull requests. (We really wanted to switch over to the OpenSSL implementation rather than shipping our own, in part because ours was depending on some OpenSSL AES primitives that OpenSSL recently deprecated for external users.)

Maybe one lesson here is that many people believe in the benefits of unit tests for their own code, but we're not as thorough or experienced in writing acceptance tests for our dependencies.

Mosh got lucky this time that we had pretty good tests that exercised the library enough to find this bug, and we run them as part of the package build, but it's not that farfetched to imagine that we might have users on a platform that we don't build a package for (and therefore don't run our testsuite on).

這有點有趣 XDDD

Brendan Gregg 加入 Intel

先前有提到 Brendan Gregg 離開了 Netflix 的事情:「Brendan Gregg 離開 Netflix」,剛剛看到他發表他去 Intel 的消息:「Brendan@Intel.com」。

看起來是任何跟 performance 有關的都可以碰,但主力會放在跟 cloud 相關的產品線上:

I'm thrilled to be joining Intel to work on the performance of everything, apps to metal, with a focus on cloud computing.

不知道起頭會碰什麼東西,也許先花幾個月熟悉?

用 objdump 學到的一些東西...

Hacker News 首頁上看到「Hand-optimizing the TCC code generator (briancallahan.net)」這則,原始文章在「Hand-optimizing the TCC code generator」這邊。

主要是在文章內看到 objdump 這個東西,作者用這兩個指令看組語:

tcc -c true.c
objdump -d true.o

另外同樣道理也可以用 gcc -c true.cGCC 轉出來的版本。

倒出來的組語是 AT&T 語法,但我熟悉的是 Intel 語法,對我的直覺上需要習慣... 另外我看了一下 GCC 編出來的組語:

0000000000000000 <main>:
   0:   f3 0f 1e fa             endbr64 
   4:   55                      push   %rbp
   5:   48 89 e5                mov    %rsp,%rbp
   8:   b8 00 00 00 00          mov    $0x0,%eax
   d:   5d                      pop    %rbp
   e:   c3                      retq

第一行的那個 endbr64 指令沒看過,查一下發現原來是 Intel 在 CPU 層設計出來的安全機制,標示這個地方可以被 indirect call 進來:「What does the endbr64 instruction actually do?」。

至於文章裡面主要提到的 mov $0x0, %eax 可以用 xor %eax, %eax 代替 (或是 sub %eax, %eax) 算是很久前就會的東西了...

從三角函數 cosine 的實做問題學一些週邊知識...

前幾天在 Hacker News 上看到「Implementing Cosine in C from Scratch (2020) (austinhenley.com)」這篇 2020 的文章,原文是「Implementing cosine in C from scratch」,裡面內在講自己刻三角函數的 cosine 所遇到的一些嘗試。

cosine 是很基本的函數,所以可以使用的地方很多。另外一方面,也因為他不是那麼直覺就可以實做出來,在現代的實做裡面其實藏了超多細節...

不過真的有趣的是在翻 Hacker News 上的討論時陸陸續續翻其他的資料看到的知識。

第一個看到的是 Intel 對於 FPU-based 指令集內的 FSIN 因為 π 的精度不夠而導致誤差超大 (尤其是在 0 點附近的時候):「Intel Underestimates Error Bounds by 1.3 quintillion」,然後 AMD 是「相容」到底,所以一樣慘:「Accuracy of FSIN and other x87 trigonometric instructions on AMD processors」。

這個就是有印象,但是太久沒有提到就會忘記...

第二個是 musl libc 裡的 cosine 實做 (看註解應該是從 FreeBSD 的 libc 移植過來的?):「__cos.c\math\src」與「cos.c\math\src」(話說 cgit 在 html 內 title 的內容對路徑的表達方式頗有趣,居然是反過來放...)。

拆開的部份是先將範圍限制在 [-\pi/4, \pi/4] 後 (這個部份看起來是透過 __rem_pio2.c 處理),再丟進公式實際運算。

另外帶出來第三個知識,查資料的時候翻到 binary64 (這也是 C 語言裡面的 double) 與 binary128 的差異:

而大家很常拿來惡搞的 double double 則是利用兩個 double 存放,形式是 v = head + tail,利用不同的 exponent 表示來不同部份的值,以提高經度:

A common software technique to implement nearly quadruple precision using pairs of double-precision values is sometimes called double-double arithmetic.

不過這樣的精確度只能到 106 bits,雖然跟 binary128 能達到的 113 bits 相比低了一些,但在大多數的情況下也還算夠用:

Using pairs of IEEE double-precision values with 53-bit significands, double-double arithmetic provides operations on numbers with significands of at least[4] 2 × 53 = 106 bits (...), only slightly less precise than the 113-bit significand of IEEE binary128 quadruple precision.

立端科技的 IIoT-I530

因為工作的關係,所以會關注一些特殊的硬體,但好像暫時找不到地方放,就丟在 blog 上面記錄好了...

這次看到的是支援一堆 PoE+ 的機器:「Tiger Lake-U system features dual 2.5GbE and six PoE+ ports」。

除了 PoE+ 以外另外有 mSATASATA 支援,然後還有一堆 M.2 的界面可以接 (好像是走 PCIe):

Lanner’s “IIoT-I530” embedded PC runs Linux on an 11th Gen U-series CPU and supplies with up to 64GB RAM, 2x 2.5GbE, 6x PoE+, 2x COM, 4x USB 3.0, 2x HDMI, 3x M.2, SATA, mSATA, and DIO.

來看 Intel + Varnish 的單機 500Gbps 的 PR 新聞稿

在「Varnish Software Achieves 500Gbps Throughput Per Server for UHD Video Content」這邊看到 PR 稿,由 IntelVarnish 合作,宣稱達到單機 500Gbps 的 throughput 了:

According to Varnish Software, the following were the outcomes of the test:

  • 509.7 Gbps live-linear throughput, using a dual-processor configuration
  • 487.2 Gbps video-on-demand throughput, using a dual-processor configuration

白皮書在「Delivering up to 500 Gbps Throughput for Next-Gen CDNs」這頁可以用個資交換下載,不過用搜尋引擎找一下可以發現 Intel 那邊有放出 PDF (但不確定兩邊給的是不是同一份):「Delivering up to 500 Gbps Throughput for Next-Gen CDNs」。

單 CPU 的伺服器是四個 100Gbps 界面接出來,雙 CPU 的伺服器是八個 (這邊 SUT 是 system under test 的縮寫):

These client systems were connected to the CDN servers using 100 GbE links through a switch; 4x100 GbE connections for the single-processor SUT, and 8x100 GbE for the dualprocessor SUT. Testing was done using Wrk, a widely recognized open-source HTTP(S) benchmarking tool.

不過如果實際看圖會發現伺服器是兩個 100Gbps (單 CPU) 與四個 100Gbps (雙 CPU),然後 wrk 也吃了兩個或是四個 100Gbps:

在白皮書最後面也有提到測試的配置,都是在 Ubuntu 20.04 上面跑,單 CPU 用的是兩張 Intel 的 100Gbps 網卡,雙 CPU 的用的是四張 Mellanox 的 100Gbps 網卡:

3rd generation Intel Xeon Scalable testing done by Intel in September 2021. Single processor SUT configuration was based on the Supermicro SMC 110P-WTR-TNR single socket server based on Intel® Xeon® Platinum 8380 processor (microcode: 0xd000280) with 40 cores operating at 2.3 GHz. The server featured 256 GB of RAM. Intel® Hyper-Threading Technology was enabled, as was Intel® Turbo Boost Technology 2.0. Platform controller hub was the Intel C620. NUMA balancing was enabled. BIOS version was 1.1. Network connectivity was provided by two 100 GbE Intel® Ethernet Network Adapters E810. 1.2 TB of boot storage was available via an Intel SSD. Application storage totaled 3.84TB per drive and was provided by 8 Intel P5510 SSDs. The operating system was Ubuntu Linux release 20.04 LTS with kernel 5.4.0-80 generic. Compiler GCC was version 9.3.0. The workload was wrk/master (April 17, 2019), and the version of Varnish was varnishplus-6.0.8r3. Openssl v1.1.1h was also used. All traffic from clients to SUT was encrypted via TLS.

3rd generation Intel Xeon Scalable testing done by Intel in September 2021. Dual processor SUT configuration was based on the Supermicro SMC 22OU-TNR dual socket server based on Intel® Xeon® Platinum 8380 processor (microcode: 0xd000280) with 40 cores operating at 2.3 GHz. The server featured 256 GB of RAM. Intel® Hyper-Threading Technology was enabled, as was Intel® Turbo Boost Technology 2.0. Platform controller hub was the Intel C620. NUMA balancing was enabled. BIOS version was 1.1. Network connectivity was provided by four 100 GbE Mellanox MCX516A-CDAT adapters. 1.2 TB of boot storage was available via an Intel SSD. Application storage totaled 3.84TB per drive and was provided by 12 Intel P5510 SSDs. The operating system was Ubuntu Linux release 20.04 LTS with kernel 5.4.0-80- generic. Compiler GCC was version 9.3.0. The workload was wrk/master (April 17, 2019), and the version of Varnish was varnish-plus6.0.8r3. Openssl v1.1.1h was also used. All traffic from clients to SUT was encrypted via TLS.

不過馬上就會滿頭問號,四張 100Gbps 是怎麼跑到 500Gbps 的頻寬...

這份 PR 馬上就讓人想到 Netflix 先前放出來的投影片 (先前有在「Netflix 在單機服務 400Gbps 的影音流量」這篇提到),在 Netflix 的投影片裡面有提到他們在 Intel 平台上面受限於記憶體的頻寬,整台機器只能跑到 230Gbps。

另外一種猜測是,如果 Intel 與 Varnish 宣稱的 500Gbps 是算 switch 上的總流量 (有這樣算的嗎,你是 Juniper 嗎...),那這邊的 500Gbps 換算回去差不多就是減半 (還很客氣的沒把 cache 沒中需要去 origin server 拉資料的流量扣掉),跟 Netflix 在 FreeBSD 上跑出來的結果差不多啊...

坐等反駁 XDDD

在 Linux (Ubuntu) 上跑透過 QEMU 跑 Windows/Mac/Linux 的工具

Hacker News Daily 上看到的工具:「Quickly create and run optimised Windows, macOS and Linux desktop virtual machines.」,對應的討論在「Quickemu: Quickly create and run optimised Win-10,11/macOS/Linux on Linux (github.com/wimpysworld)」這邊可以看到,可以減少自己要設定一堆 QEMU 參數。

雖然專案是支援多系統,但其實 Microsoft WindowsLinux 的部份在其他虛擬軟體都很簡單 (像是用 VirtaulBox),大家馬上會注意到的重點還是 macOS 的部份,如果有自己弄過就會知道這東西有夠難裝的,而且跨版本有不同的安裝方式...

目前 Quickemu 支援四個版本:

Supported macOS releases:

  • High Sierra
  • Mojave
  • Catalina (Recommended)
  • Big Sur

然後可以看到幾乎所有目前能支援的功能都有設定上去了,包括 VirtIO 與 USB 的部份。

然後一些經典的問題,像是 Big Sur 的音源問題還是沒解:

Full Duplex audio works on macOS High Sierra, Mojave and Catalina.

  • macOS Big Sur has no audio at all.

在 Hacker News 的討論串裡面有提到有很多地方沒有檢查,這會是風險:

While I appreciate the effort, and the code is very readable. I just want to give a friendly warning that these shell scripts just download random stuff from the internet and run this random stuff without checking any integrity/signature.

下面的討論另外看到個冷知識,關於蘋果故意走 HTTP 下載 recovery image 是因為 HTTPS 太複雜,在 UEFI firmware 裡面實做容易產生被攻擊的點,所以決定自己透過其他機制確認正確性:

Apple Internet recoveryOS images are served over plain http, on purpose. The macrecovery.py script used by Quickemu uses http¹, though the server supports https.

https://support.apple.com/guide/security/recoveryos-and-diagnostics-environments-sec2512a0c09/web

> When the internet recovery and diagnostic modes were added to Mac computers in 2011, it was decided that it would be better to use the simpler HTTP transport, and handle content authentication using the chunklist mechanism, rather than implement the more complicated HTTPS functionality in the UEFI firmware, and thus increase the firmwareʼs attack surface.

¹https://github.com/acidanthera/OpenCorePkg/blob/4a740c3f256e285c66ca3b65e42b60af6826d343/Utilities/macrecovery/macrecovery.py#L123

[edit] Added macrecovery.py info

另外為了避免直接在 shell script 裡面出現「神秘字串」,可以看到特別的寫法 XDDD

Took a little while to find the magic words in there: https://github.com/wimpysworld/quickemu/blob/af26f41440d63a069045660fad860c797011310a/quickemu#L351

可以想到一些用途,像是在機房裡面跑 CI 的 worker,但要注意這個搞法不符合蘋果的 EULA,現在不抓不代表以後也不會有事,請自己謹慎評估...

然後往 ARM-based 架構後應該門檻就更高了,現在還有 Intel-based 的環境可以用加減用...

Netflix 在單機服務 400Gbps 的影音流量

Hacker News 首頁上看到 NetflixEuroBSDCon 2021 上發表的投影片:「Serving Netflix Video at 400Gb/s on FreeBSD」,對應的討論則是在「Serving Netflix Video at 400Gb/s [pdf] (freebsd.org)」這邊可以翻到,投影片的作者有在上面回答一些問題。

投影片在講的應該就是 Netflix 的 Open Connect

主要是因為 Open Connect 的伺服器是放到各家 ISP 機房,在單一 IP 且單一伺服器的限制下,要想辦法壓榨出最高的效能。

硬體是 AMDEPYC,在先前的版本可以達到 240Gbps,經過分析與嘗試解決了一堆問題後,最後是在原來的 AMD 機器上跑到了 380Gbps (另外有測 ARM 以及 Intel 的數字),然後之後機房有可能會有 800Gbps 的標準,他們又要繼續煩惱...

有看到 Mellanox ConnectX-6 Dx (CX6-DX) 這個東西,看起來很有趣啊,有 200Gbps 的能力,而且可以把 TLS 的事情推到卡上面處理... 然後這家公司被 Nvidia 買走了。

另外當然也會有人問為什麼不用 Linux,作者在討論串裡面也有回答一些,有興趣的可以自己去搜一下。

Intel 與 AMD 在 RSQRTSS 的不同

看到「rr Trace Portability: Diverging Behavior of RSQRTSS in AMD vs Intel」這個,作者因為在 rr 上發現 replay 不正確,發現是 SSE 裡面的 RSQRTSS 這個指令在 IntelAMD 平台上會有不同的值出現導致的。

RSQRTSS 是計算平方根倒數,也就是計算 1 / \sqrt{x},另外比較特別的是,這個指令不保證正確性,是允許有誤差產生的。

提到平方根倒數,這個演算法更有名的應該是「反平方根快速演算法」這個用到 0x5f3759df 這個魔術數字的奇技淫巧,不過這不是這次的重點...

作者發現 RSQRTSS 在 Intel 與 AMD 平台的值不一定一樣,像是 256 的平方根導數是 1/16 (0.0625),但兩個平台跑出來不同:

On Intel Skylake I get
out = 3d7ff000, float = 0.062485

On AMD Rome I get
out = 3d7ff800, float = 0.062492

在這邊的 case 可以看出來 AMD 算的比較正確 (誤差值比較低),但都還是在 spec 允許的誤差範圍。

後來作者還發現有其他不同的指令也有類似的問題,為了解決在 rr 上可以正確 replay 的問題,他生了對應的 mapping table 來解:「Emulating AMD Approximate Arithmetic Instructions On Intel」。

苦啊... 不過這個主題還蠻有趣的。