Raspberry Pi 4 - fast enough for a desktop?

But who uses a Pi for that?

I certainly did not.

I know that. But who else does?

People who are interested enough in assembly language to learn some of the associated terminology.

(People are aren?t interested in assembly presumably don?t care about the detailed differences between instruction sets.)

Ok, but there is a lot of assumption in there :-)

E.g. I used to do assembler programming (long ago) but only after saw the explanation did I go: ah yes.

This brings us to an important rule of writing: if you're going to use an acronym or abbreviation - especially if it's not in wide use - write it out in full the first time, preferably followed by the abbreviation in parentheses. Afterwards you can use the abbreviation alone and the reader will be sure to know what it means.

If you're only using the term once, don't waste your (or the reader's) time by abbreviating it at all.

Exactly. I've done loads of assembler, and know what general purpose registers are but I had to think a bit before I associated 'GPR' with them.

Anyway beck to the thread: I stand by my statement that unless you are masively compute bound running a 32 bit OS wont slow you down too much, you only have 4GB to address anyway, so no need for 64 bit there, and in reality whacking in an SSD is probably all you need to do to get a very acceptable general purposes desktop system

And of couyrse its not erleavant to an absteraqct discussion about 64 bit processors, since its is ARM specific (and maybe one or tow others).

embler.

Don't expect general performance gains with 64bit ARM. It's only because

x86 is such an atrocious outdated mess, that the AMD64 instruction set shows significant gains. On every other architecture supporting both 32 bit and 64 bit code (Power, Sparc, MIPS) the 64 bit code is usually slower than the 32 bit on the same chip, due to the increased demand on the data cache from 64 bit pointers.

With the current state of ARMv8 support on GCC, CPU and memory bound programs vary from a barely noticeable few percent drop, to 50% slower. So it only makes sense to move from running 32 bit to 64 bit code when moving to a chip with which supports 4GB or more of memory, and a much larger data cache.

---druck

And, of course, if you?re massively compute-bound you aren?t spending much time in the OS, so that?s not an issue.

Umm. Can a 32 bit OS run 64 bit programs?

Or when all new chips are coming out with 64 bit instruction sets and it becomes clear that 32 bit instruction sets will no longer be supported by new processors as from some date in the quite near future.

Which is where we are now.

David

No that isn't possible as a 32 bit OS can't set up the required 64 bit configuration. But a 64 bit OS can run both 64 bit and 32 bit programs.

There is also a mode called ILP32, which uses the 64 bit ARMv8 instruction set, but 32 bit longs and pointers. So you get the benefits of the improved instruction set (more registers, better branch prediction), but avoid the disadvantage of increased cache when dealing with 64 bit values.

The only drawback is you need a complete set of ILP32 compiled userland libraries, nearly doubling the size of your OS image (or adding another

---druck

Only some licencees high end server class ARMv8A cores are 64 bit only, where there is no need of backwards compatibility. One of ARM's general purpose cores (A72) now only support 64 bit privileged modes, but 32 bit userland is still supported for running legacy code. The Pi 4's A72 supports both 32 and 64 bit OSs and userlands.

Support for 32 bit ARM isn't going to disappear as (hopefully) 32bit x86 will do soon, as billions of 32 bit ARM chips are still be used for low power applications, which wont gain anything from 64 bits.

---druck

Storage is cheap, especially in terms of the size of an OS image.

On Tue, 02 Jul 2019 14:19:21 +0100, David Higton declaimed the following:

Except so many ARM processors implement Thumb(2) which is a 16-bit wide instruction set (for 32-bit accesses)

That is what I thought.

So unless you are coding in assembler, your system calls will dictate using a 32 bit instruction set.

Very interesting.

Less room for ASLR would be the other drawback.

There?s a similar thing in the Intel Linux world, call X32. I?ve never heard of anyone using it in anger...

Hi I've just tried using a Pi 4 4GB under Raspbian. The answer is that whilst it is undoubtedly very impressive it isn't good enough for a general purpose desktop.

The good:

• Chromium browsing not featuring video was good. Perhaps a bit slow but not annoyingly so.

• vlc could play x264 video perfectly at 1080p, at about 5% cpu.

• Generally apps/windows opened at an OK speed.

The bad:

• vlc was poor at playing x265 at 1080p, jerky, 50% cpu and about 30% dropped frames.

• Youtube video was awful, slow, jerky. As were other, popular, free video Streaming sites.

• Amazon Video wouldn't play at all due to chromium not being a supported browser.

• LibreOffice Calc gave painfully slow scrolling, on a sheet with 365 rows and 26 columns.

General comments. The main problem seems to be applications lacking support for hardware video decoding and maybe also a lack of GPU support. In particular Chromium doesn't seem to be doing video efficiently.

So I will use this Pi as a server rather than a desktop.

On 02/07/2019 21:29, druck wrote:> Only some licencees high end server class ARMv8A cores are 64 bit only,

Correction; that should be the A76, which has 64 bit only privileged modes.

---druck