bremac · HackerTrans

bremac

no profile record

Submissions

Correctly-rounded evaluation of a function: why, how, and at what cost? [pdf]

hal.science

2 pointsby bremac2 ปีที่แล้ว0 comments

At the restaurant of the future, tablets take your order

theatlantic.com

46 pointsby bremac14 ปีที่แล้ว58 comments

Can Color-Blind Users See Your Site?

msdn.microsoft.com

5 pointsby bremac15 ปีที่แล้ว2 comments

comments

ปีที่แล้วdiscuss

Location: San Francisco, CA

Remote: Yes

Willing to relocate: Yes

Technologies: Java, C, C++, SQL, Python, Kubernetes, Linux, perf, PostgreSQL, OCaml

Résumé/CV: http://macdonell.net/resume.pdf

Email: [email protected]

Staff engineer with over a decade of experience leading products to successful delivery and beyond. Recently focused on high-performance streaming analytics at Sight Machine (I led the design and implementation of their stream processing engine, and before that, their data acquisition product), I can also work as a generalist backend developer or team lead.

Shoot me an email if you want to chat!

2 ปีที่แล้วdiscuss

  Location: San Francisco, CA
  Remote: Yes
  Willing to relocate: Yes
  Technologies: Java, C, C++, SQL, Python, Kubernetes, Linux, perf, PostgreSQL, OCaml
  Résumé/CV: http://macdonell.net/resume.pdf
  Email: [email protected]

Staff engineer with over a decade of experience leading products to successful delivery and beyond. Recently focused on high-performance streaming analytics at Sight Machine (I led the design and implementation of their stream processing product, and before that, their data acquisition product), I can also work as a generalist backend developer or team lead.

Shoot me an email if you want to chat.

No management positions, please!

2 ปีที่แล้วdiscuss

Unfortunately none of the hardware used for testing supports FP16 arithmetic. Between Intel and AMD, the only platform that supports AVX512-FP16 is currently Sapphire Rapids.

2 ปีที่แล้วdiscuss

Value types still require allocation for types larger than 128 bits if the value is either nullable or atomic — that seems like a reasonable trade-off to me.

2 ปีที่แล้วdiscuss

Keep in mind that you still need send a print job to the fake printer to trigger the exploit. If you send the job to your real printer, nothing happens.

2 ปีที่แล้วdiscuss

Per the bug report, all versions since Java 8 are affected.

3 ปีที่แล้วdiscuss

Unfortunately, unless the JIT can prove that the address you are accessing via the segment is non-negative, it can't elide the bounds check. See https://mail.openjdk.org/pipermail/panama-dev/2023-July/0194... for a bit more information.

3 ปีที่แล้วdiscuss

As the comment you replied to indicates, both of those APIs perform bounds-checking. In certain tight loops, this can add up to quite a bit of overhead [1]. However, it's not documented, but if you really know what you are doing you can convince the JIT to elide the bounds checks for MemorySegments [2].

[1] https://mail.openjdk.org/pipermail/panama-dev/2023-July/0193...

[2] https://mail.openjdk.org/pipermail/panama-dev/2023-July/0194...

3 ปีที่แล้วdiscuss

Reading between the lines, it sounds as if they're using mmap. There is no "append" operation on a memory mapping, so the file would need to be preallocated before mapping it.

If the preallocation is done using fallocate or just writing zeros, then by default it's backed by blocks on disk, and readahead must hit the disk since there is data there. On the other hand, preallocating with fallocate using FALLOC_FL_ZERO_RANGE or (often) with ftruncate() will just update the logical file length, and even if readahead is triggered it won't actually hit the disk.

3 ปีที่แล้วdiscuss

I think you may have linked to the wrong graph — while that graph does have a spike on it, the spike happens when the index was broadened in May 2020 to include savings and money market accounts.

4 ปีที่แล้วdiscuss

Thanks for mentioning this, I couldn't think of where I'd read about this technique before. I was remembering https://webkit.org/blog/6161/locking-in-webkit/

4 ปีที่แล้วdiscuss

I think that the answer here is "not easily". To use the x32 ABI, you would need:

1. Kernel support to be enabled in order to make x32 system calls. Checking /proc/config.gz on Arch Linux, my kernel does not appear to have it enabled.

2. An x32 toolchain to build against. For gcc and glibc, that would mean re-compiling as described here: https://sourceware.org/glibc/wiki/x32

3. All of the libraries you link with to be recompiled for the x32 ABI.

x86 is definitely easier to build against since there's still legacy software using it, whereas almost nobody seems to use x32. However, over the long term I expect x86 compatibility will bit-rot too.

4 ปีที่แล้วdiscuss

> If you allocate a chunk on the heap with 8-byte alignment, then you can throw away the lowest 3 bits of precision, and then you can address 32GB with a 32-bit pointer.

This part is totally doable, and in fact it's one of the pointer compression modes built into the JVM: https://shipilev.net/jvm/anatomy-quarks/23-compressed-refere...

For C++, it's a really interesting thought experiment, but in practice there are a few rough edges:

1. Your debugging tools will probably struggle to interpret compressed pointers.

2. You'll need to roll your own containers too. Otherwise, vectors, strings, maps, smart pointers, etc. will still use 64-bit pointers. In my experience, containers account for most pointers in a modern C++ code base.

3. _Technically_, the representation of null pointers is implementation-defined, so truncating to 32 bits and then zero-extending is not portable: it could convert a null pointer to a non-null pointer. In practice it doesn't matter though, since every modern target uses a zero bit pattern for null pointers.

4 ปีที่แล้วdiscuss

-m32 doesn't target the x32 ABI though, it targets x86. Per the manual:

> The -m32 option sets int, long, and pointer types to 32 bits, and generates code that runs on any i386 system.

That restricts you to the smaller register set, removes all amd64 instructions, and uses the x86 ABI (on Linux, parameters are passed on the stack instead of in registers.) I suspect that this is why your program became slower, as opposed to using 32-bit pointers.

4 ปีที่แล้วdiscuss

I'm unsure about library support, but gcc and clang support function multi-versioning (FMV), which resolves the function based on CPUID the first time the function is called.

This LWN article has some additional information: https://lwn.net/Articles/691932/

4 ปีที่แล้วdiscuss

> but interests of corporate mega producers they can't guarantee such thing at scale. So to protect them and people from them these laws are made kind of impossible triangle.

In North America, many of these laws were passed in the early part of the 1900s [1]. I don't think that were very many mega producers at the time, though I'd love to be proven wrong.

Also in my experience it's really hard to avoid contamination. My family farm works hard to keep their cows healthy, happy, and clean, and still has occasional issues with high somatic cell counts in their milk. It doesn't help that cows will (rarely) decide to release their bowels while you're milking them...

[1] https://www.marlerblog.com/lawyer-oped/a-legal-history-of-ra...

4 ปีที่แล้วdiscuss

As someone who grew up on a dairy farm, who worked on a farm, and who has friends and family operating their own farms, I'd like to point out that this is backwards. Farmers know that bacteria can make them sick or even kill them. It's the city-slickers who have never been truly ill who think that they're harmless.

4 ปีที่แล้วdiscuss

As much as I am not a fan of Applebee's, the article title on HN should probably be fixed. The executive who sent the email works for Apple Central, a mid-sized franchisee with less than fifty locations. They do not work for Applebee's itself, nor do they represent a major franchisee. (Though in this case, it sounds like their views aren't even representative of their own franchise.)

4 ปีที่แล้วdiscuss

The internet is the least of your problems. The key industrial automation equipment (PLCs and IPCs) is connected directly to your machines. Higher-level control and planning functions like MES and SCADA are usually running from your server closet. You might not have access to your ERP or cloud MES system, but you can keep the lines running without them for a while. Plenty of factories have weak or flaky internet, so operating during an internet outage is hardly a novel situation.

Your bigger problem is the supply chain. After the apocalypse, I doubt you'll have an easy time sourcing cans, bulk product, spare parts, and sanitizer to run your factory. After all, each of those inputs to your process have their own complex supply chain too. And no, you're not really going to be able to scavenge these parts of manufacture them yourself, since they all have fairly fine tolerances.

In reality, I'd expect that an apocalypse will cause a reversion to a more subsistence-style lifestyle, where production and consumption are largely local and supply chains are very simple, if present at all. Computers will not help with this. I can't imagine keeping our current production processes running without all of the things required to support them.

4 ปีที่แล้วdiscuss

If Putin presses on toward Poland or threatens the Baltics, then we will be on a knife's edge. However, for now, Russia has only invaded Ukraine. It's a humanitarian disaster, but so far on the world stage it shows no sign it will escalate beyond new sanctions, export controls, and perhaps additional military support for NATO members in Eastern Europe.