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A preview of x64 emulation on Windows for ARM

blogs.windows.com

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Re: A preview of x64 emulation on Windows for ARM

#311

Post by sharpneli »

haberman wrote: post #262
sharpneli wrote: post #124

Earlier quoted context omitted.

Another major difference is the memory model. In X86 other CPU’s must always see the writes of a core exactly in the right order. This limits the ability to reorder store ops significantly. ARM requires a memory barrier for this. This is a major reason why X86 emulation is so slow. One must basically issue a memory barrier after every store op. M1 actually also implements the X86 memory model too in HW. It’s only usa…

I am trying to wrap my head around whether ARM's looser memory model is a fundamental performance advantage or not. I had always assumed that the looser memory model must have a performance benefit. But this comment from last week argues that it doesn't really buy that much, and that a bigger buffer can eliminate most of the difference: https://news.ycombinator.com/item?id=25263461 If TSO forces flushing of store buf…

It has to flush them. Because if another core sees the result of the atomic op it must also see everything else that the other core wrote before the op. While it can indeed first see no writes and then suddenly all it can never see just the atomic op and not the previous writes.

Without that the store buffers can be kept unflushed to, as an example, see if one can get a full cacheline or whatnot and only flush then.

The comment is correct that an X86 with heavy reordering backend will beat arm without one. However arm with one does handily beat X86 with one. Case in point: M1

Re: A preview of x64 emulation on Windows for ARM

#312

Post by tambourine_man »

sonotmyname wrote: post #265
ksec wrote: post #127

Earlier quoted context omitted.

AH! Thank You. The timeline make sense. Seems Apple have time this perfectly for their transition. I am now giving them some creditable excuses for the negligence of Mac in the past few years.

> Seems Apple have time this perfectly for their transition Important to note that this doesn't really apply to Apple Silicon. Rosetta II isn't X86 emulation, it's a translation layer - big technical difference.

I get the technical difference but not the legal one. Why would one be OK but not the other?

Re: A preview of x64 emulation on Windows for ARM

#313

Post by sharpneli »

annilt wrote: post #291
sharpneli wrote: post #124

Earlier quoted context omitted.

Another major difference is the memory model. In X86 other CPU’s must always see the writes of a core exactly in the right order. This limits the ability to reorder store ops significantly. ARM requires a memory barrier for this. This is a major reason why X86 emulation is so slow. One must basically issue a memory barrier after every store op. M1 actually also implements the X86 memory model too in HW. It’s only usa…

Just want to add one thing, x86 has stronger memory “semantics”. So, it doesn’t have to work that way behind the scenes, just at the end of the block, it has to appear it worked that way. So, x86 does reordering, store combining etc a lot. IMHO, performance difference between arm vs x86 barely related with ISA, in M1 case, it’s definitely not, a lot more going on than just taking advantage of weaker memory model.

Having to appear worked that way does cause restrictions in multiprocessor case. ARM chips naturally do all of that too, with the memory model simply giving them way more freedom to reorder things.

One couldn’t do X86 version of M1, mostly because there is no way of making an instruction decoder that wide for it.

And the performance penalty of M1 when working in TSO mode strongly implies that yes the weaker memory model indeed plays a major role. Not the biggest, but definitely not insignificant. Tens of percents here and tens of percents there combined become a ridiculous perf boost.

Re: A preview of x64 emulation on Windows for ARM

#314

Post by wayneftw »

whatever1 wrote: post #132

Now we need an ARM processor that can compete with M1. Seems that Apple caught everyone with the pants down in the PC industry. Microsoft SQ2 processor that ships in their $1400 Surface Pro X is almost 50% slower than M1.

> ...Apple caught everyone with the pants down in the PC industry...

Pffft. There's no competition between PCs and Apple, they're not even in the same class. PCs are general purpose computers and Apple products are closed platform devices that you don't really own or have any control over.

That's why Macs only have 10% the market size of PCs.

Re: A preview of x64 emulation on Windows for ARM

#315

Post by x87678r »

emilsedgh wrote: post #7

I'm wondering what's happening at Microsoft's camp regarding M1. They are in a weird situation. They depend on AMD/Intel to deliver. This is a massive dependency for Microsoft. Are there other large corporations have this big of a dependency? I understand that Microsoft's revenue is shifting towards cloud, services, etc. But I think Windows is still "the" key to a lot of those offerings. Take a massive chunk of marke…

I think MS is in trouble. Nearly everyone's home computer just runs Chrome now. Work PCs are going the same direction. Even developers can probably rely on a SSH and RDP to a server running anything. Android tablets are selling for about the same price as Windows license.

Re: A preview of x64 emulation on Windows for ARM

#316

Post by romanoderoma »

bfgoodrich wrote: post #217
pjmlp wrote: post #205

Earlier quoted context omitted.

I bet if we do a demographic IP check that is what most HN logins come from. I surely do, whatever Porsche and Ferrari do have very little repercussions on the automotive market, if you want a comparison.

This circular logic is more disingenuous noise (the userbase of HN is utterly irrelevant given that you're trying to prove your own absurd claim that only HN cares, when clearly the entire developed world cares). How are you not moderated down to transparent by now? [I will tell you why - because the title draws in a certain crowd that is comforted by your nonsense, however fictional it is] Whatever you hope the posi…

> Apple -- at 20% or so in most of the world's economies

Apple has 17% (and dropping) of the mobile market share in Europe and around 9% in computing.

There aren't many other richer economies in the World.

Ferrari is worth now more than General Motors and Ford, so market share and net worth are not comparable.

Their market share is small because they make a luxury limited edition product.

They limit their production capacity to around 10 thousands cars/year (all sold in pre order), Apple is trying to sell as many devices they can.

There are no Ferrari Store where you can buy a Ferrari and drive it home half an hour later.

It's not a small difference.

Last but not least, there is a lot more competition between car manufacturers, even in the most expensive segments, Apple devices are only made by Apple.

Hyundai, for example, had a net income of over 3 trillion in 2019, Apple net income is measured in tens of billions.

Re: A preview of x64 emulation on Windows for ARM

#317

Post by supernovae »

x87678r wrote: post #315
emilsedgh wrote: post #7

I'm wondering what's happening at Microsoft's camp regarding M1. They are in a weird situation. They depend on AMD/Intel to deliver. This is a massive dependency for Microsoft. Are there other large corporations have this big of a dependency? I understand that Microsoft's revenue is shifting towards cloud, services, etc. But I think Windows is still "the" key to a lot of those offerings. Take a massive chunk of marke…

I think MS is in trouble. Nearly everyone's home computer just runs Chrome now. Work PCs are going the same direction. Even developers can probably rely on a SSH and RDP to a server running anything. Android tablets are selling for about the same price as Windows license.

PC/Laptop and Microsoft are thriving. You can't even buy a modern GPU from AMD or Nvidia and Ryzen cpus are sold out everywhere - and there is a massive new console launch with X86 on new Xbox and PS5.

Windows has supported ARM for a while and they have a nice arm device right now.

New mobile Ryzen chips are extremely fast and efficient. X86 isn't going anywhere.

If Apple is successful putting algorithms into silicon for micro efficiencies Intel/AMD/Microsoft aren't going to sit idly by.

Re: A preview of x64 emulation on Windows for ARM

#318

Post by cptskippy »

xmodem wrote: post #194
TheRealDunkirk wrote: post #158

Earlier quoted context omitted.

It would be hard to argue that the PC world won't at least make some attempt at shifting to ARM. Apple has demonstrated far too large of a performance and power efficiency savings to not try. Of course, even if that becomes successful, x86 will be available for decades. Right now, ARM Macs are going to just be lost for any kind of gaming (except Catalyst versions of mobile games). This is probably ridiculous, but my…

> ARM Macs are going to just be lost for any kind of gaming Every game I've tried with a Mac port runs great on the M1 under Rosetta. I've sunk many hours into Factorio and Offworld Trading Company on my M1 mini, and if I gave you the same game running side by side on an Intel mac, I'd bet you could't tell which was which without quitting and checking the system profiler. If you meant triple-A gaming, then yeah, with…

Those are very niche games with very low system requirements. It's a bit like saying the M1 handles emulating Solitaire and Minesweeper just fine.

Re: A preview of x64 emulation on Windows for ARM

#319

Post by bfgoodrich »

romanoderoma wrote: post #316
bfgoodrich wrote: post #217

Earlier quoted context omitted.

This circular logic is more disingenuous noise (the userbase of HN is utterly irrelevant given that you're trying to prove your own absurd claim that only HN cares, when clearly the entire developed world cares). How are you not moderated down to transparent by now? [I will tell you why - because the title draws in a certain crowd that is comforted by your nonsense, however fictional it is] Whatever you hope the posi…

> Apple -- at 20% or so in most of the world's economies Apple has 17% (and dropping) of the mobile market share in Europe and around 9% in computing. There aren't many other richer economies in the World. Ferrari is worth now more than General Motors and Ford, so market share and net worth are not comparable. Their market share is small because they make a luxury limited edition product. They limit their production…

This is so intensely boring and stupid.

Firstly, you profoundly misunderstood the inclusion of Ferrari, hilariously trying to twist that into an Apple critique.

Secondly, Apple is selling as many or more iPhones than ever in Europe (19% in the EU). And Japan. And the US. And Canada. And Australia. And CHINA. And Singapore. And South Korea. Literally every rich area on Earth.

Contrasted with pjmlp's "only the US" (actually the HN "bubble").

This has turned into farce. Carry on with the nonsense.

Re: A preview of x64 emulation on Windows for ARM

#320

Post by cogman10 »

0xffff2 wrote: post #282
cogman10 wrote: post #269

Earlier quoted context omitted.

Brexit is in a constant state of happening and not happening. You can think of it like a qubit.

That was true for a long time, but to quote the Government of the Netherlands (the closest thing I can find to an official source) [0]: >The United Kingdom (UK) left the European Union (EU) on 31 January 2020. A transition period is now in place until 31 December 2020. As far as I can tell from my distant vantage point on the west coast of North America, there is very little doubt left. Brexit has already happened an…

We'll see what happens. I mean, it's possible that they actually end up going through with a complete exit on Dec 31. My guess, however, is that there will be ongoing negotiations for a long time to come. The UK is likely to be out but only in the sense that they don't now get to vote on EU resolutions. They'll likely make negotiations with the EU which end up putting them right back where they were (regulation wise).

That's my expectation at least. They may feel the full pain of a full exit on Dec 31, I doubt they'll want to continue in that state for very long.

There's also the possibility of yet another extension on the transition period.

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