Based on our investigation we have been able to reproduce the issue under a limited set of circumstances. We believe the issue is only present on a small number of devices with the Microsoft Teams app installed when the user is not logged in, and we are currently only aware of one user report related to the occurrence of this bug. We determined that the issue was being caused by unintended interaction between the Microsoft Teams app and the underlying Android operating system. Because this issue impacts emergency calling, both Google and Microsoft are heavily prioritizing the issue, and we expect a Microsoft Teams app update to be rolled out soon – as always we suggest users keep an eye out for app updates to ensure they are running the latest version.
In order to make it easier for AWS Partners and others to gain access to CloudWatch metrics faster and at scale, we are launching CloudWatch Metric Streams. Instead of polling (which can result in 5 to 10 minutes of latency), metrics are delivered to a Kinesis Data Firehose stream.
When you set up a stream you choose between the binary Open Telemetry 0.7 format, and the human-readable JSON format.
另外一個賣點是價位,每千次 $0.003:
Pricing – You pay $0.003 for every 1000 metric updates, and for any charges associated with the Kinesis Data Firehose. To learn more, check out the pricing page.
之前如果要自己拉出來的話是透過 API call 抓,每 1000 次是 USD$0.01,這個方法相較起來便宜不少,不過數量多的時候還是一筆費用 (而且有不少 metrics 是一分鐘更新一次)。
如果只是要備份起來或是跑分析的話,也許先前用 API 拉的作法可能還是比較好?一個小時拉一次對於備份與分析應該都很夠了,而 alarm 的機制還是掛在 CloudWatch 上。
這次產品的定位看起來是要把 ecosystem 做起來:
We designed this feature with the goal of making it easier & more efficient for AWS Partners including Datadog, Dynatrace, New Relic, Splunk, and Sumo Logic to get access to metrics so that the partners can build even better tools.
丟進 array 是 OK 的,但問題在於他需要判斷 entry 是否重複,卻沒有用 hash 或是 tree 的結構,而這邊大約有 63k 筆資料,用 array 實做就產生了 O(n^2) 的演算法:
But before it’s stored? It checks the entire array, one by one, comparing the hash of the item to see if it’s in the list or not. With ~63k entries that’s (n^2+n)/2 = (63000^2+63000)/2 = 1984531500 checks if my math is right. Most of them useless. You have unique hashes why not use a hash map.
if it’s called again within the string’s range, return cached value
而第二個問題他直接把檢查是否有重複的跳過,因為資料本身不重複:
And as for the hash-array problem, it’s more straightforward - just skip the duplicate checks entirely and insert the items directly since we know the values are unique.
I found this while making a collection of what C implementation does what at https://news.ycombinator.com/item?id=26298300.
There are two basic implementation strategies. The BSD (FreeBSD and OpenBSD and more than likely NetBSD too), Microsoft, GNU, and MUSL C libraries use one, and suffer from this; whereas the OpenWatcom, P.J. Plauger, Tru64 Unix, and my standard C libraries use another, and do not.
The 2002 report in the comp.lang.c Usenet newsgroup (listed in that discussion) is the earliest that I've found so far.
Pairing Lyra with new video compression technologies, like AV1, will allow video chats to take place, even for users connecting to the internet via a 56kbps dial-in modem.
這次的突破在於可以使用 3kbps 的頻寬傳輸,但清晰度比 Opus 的 6kbps 效果還好不少。
Google 在文章裡面給了兩個 sample,一個是乾淨背景音,另外一個是吵雜的背景音,跟 Opus 與 Speex 比起來都好很多。
We provide extensive subjective performance evaluations that show that our system based on generative modeling provides state-of-the-art coding performance at 3 kb/s for real-world speech signals at reasonable computational complexity.
Spectre 的精華在於 CPU 支援 branch prediction 與 out-of-order execution,也就是 CPU 遇到 branch 時會學習怎麼跑,這個資訊提供給 out-of-order execution 就可以大幅提昇執行速度。可以參考以前在「CPU Branch Prediction 的成本...」提到的效率問題。
原理的部份可以看這段程式碼:
這類型程式碼常常出現在現代程式的各種安全檢查上:確認 x 沒問題後再實際將資料拉出來處理。而我們可以透過不斷的丟 x 值進去,讓 CPU 學到以為都是 TRUE,而在 CPU 學壞之後,突然丟進超出範圍的 x,產生 branch misprediction,但卻已經因為 out-of-order execution 而讓 CPU 執行過 y = ... 這段指令,進而導致 cache 的內容改變。
Suppose register R1 contains a secret value. If the speculatively executed memory read of array1[R1] is a cache hit, then nothing will go on the memory bus and the read from [R2] will initiate quickly. If the read of array1[R1] is a cache miss, then the second read may take longer, resulting in different timing for the victim thread.
所以相同道理,利用乘法器被佔用的 timing attack 也可以產生攻擊:
if (false but mispredicts as true)
multiply R1, R2
multiply R3, R4
In addition, of the three user-mode serializing instructions listed by Intel, only cpuid can be used in normal code, and it destroys many registers. The mfence and lfence (but not sfence) instructions also appear to work, with the added benefit that they do not destroy register contents. Their behavior with respect to speculative execution is not defined, however, so they may not work in all CPUs or system configurations.
However, we may manipulate its generation to control speculative execution while modifying the visible, on-stack value to direct how the branch is actually retired.