Debian 的 64-bit time_t 計畫

在「Debian: 64-bit time_t transition in progress」這邊看到 Debian 的 mailing list 上的討論:「64-bit time_t transition in progress」,另外官方也有整理 wiki page:「64-bit time」。

因為技術上無法表示 2038/01/19 以後的時間,確定會 breaking ABI 將 time_t 從 32-bit 變成 64-bit,而現在要想辦法搞定 32-bit 平台上面可以處理這樣的改變:

The goal of this transition is to ensure that 32-bit architectures in trixie (whether they are currently release architectures, or out of archive, etc) will be capable of handling current and future timestamps referring to times beyond 2038.

離 2038/01/17 還有約 13 年多...

Raspberry Pi OS 64-bit 與 32-bit 的效能差異

前幾天提過「Raspberry Pi OS 64-bit 版本正式推出」,而 Phoronix 實際拿正式版測試 64-bit 與 32-bit 的系統差異了,在「Raspberry Pi OS 32-bit vs. 64-bit Performance」這邊可以看到每一個測試項目的結果。

測試的硬體是 Raspberry Pi 400,這台機器基本上就是 4GB 版本的 Raspberry Pi 4 加上週邊配件:

Using a Raspberry Pi 400 keyboard computer with 4GB of RAM, I ran some fresh benchmarks of Raspberry Pi OS in its default 32-bit build and then again with the new 64-bit build.

先講結果,在 Phoronix 的 33 個測試裡面,64-bit 全部都比 32-bit 好,而且是很明顯的差異:

Across the few dozen different workloads tested, switching Raspberry Pi OS 11 for the 64-bit version improved the performance on average by about 48%. See all the 32-bit vs. 64-bit Raspberry Pi benchmarks over on

之前 64-bit OS 還在 beta 的時候就已經知道這個情況了,所以不會覺得太意外。當時提出的解釋是指令集的差異,aarch64 提供的指令集比 armv6 有效率多了,這點在 2016 年的文章「64-bit ARM (Aarch64) Instructions Boost Performance by 15 to 30% Compared to 32-bit ARM (Aarch32) Instructions」這邊可以看到說明。

所以正式版出來以後,只要硬體有支援,基本上都建議裝 64-bit OS 了...

Raspberry Pi 4 推出 8GB 版本

Raspberry Pi 宣佈了 8GB 版本:「8GB Raspberry Pi 4 on sale now at $75」。

除了記憶體變成 8GB 以外,也因為記憶體加大而需要更多電力,所以電供元件的部份也跟著改動,然後也提到 COVID-19 造成的延遲:

To supply the slightly higher peak currents required by the new memory package, James has shuffled the power supply components on the board, removing a switch-mode power supply from the right-hand side of the board next to the USB 2.0 sockets and adding a new switcher next to the USB-C power connnector. While this was a necessary change, it ended up costing us a three-month slip, as COVID-19 disrupted the supply of inductors from the Far East.

超過 4GB 的時候一定會檢視 32-bit 與 64-bit 環境的差異,所以就會發現,在預設的 kernel 因為使用 32-bit LPAE (ARM 上的 PAE),所以雖然是有機會可以使用到 8GB,但單一程式會有 3GB 限制:

Our default operating system image uses a 32-bit LPAE kernel and a 32-bit userland. This allows multiple processes to share all 8GB of memory, subject to the restriction that no single process can use more than 3GB.

目前如果想要原生支援 64-bit 環境的話,需要使用其他作業系統:

But power users, who want to be able to map all 8GB into the address space of a single process, need a 64-bit userland. There are plenty of options already out there, including Ubuntu and Gentoo.

不過另外官方也在測自家的 64-bit 版本,已經有 early beta 版本可以測試看看了 (話說 early beta 這個詞,可以解釋成 alpha 的品質...):

Not to be left out, today we’ve released an early beta of our own 64-bit operating system image. This contains the same set of applications and the same desktop environment that you’ll find in our regular 32-bit image, but built against the Debian arm64 port.

不過上面的 ChromiumFirefox 不完整支援硬體解壓影片的部份還是痛,四代的 CPU 在 YouTube 上是可以硬撐 1080p30 解碼,但畫面順暢度就不太行了,客廳還是用老 Mac Mini (2011 的版本) 來撐場...