Learning POWER9 assembly

[MauryG5]

Guys excuse some curiosity, I read some time ago that the PowerPc instructions have been incorporated into the most recent Power ISAs, so theoretically, the old instructions that IBM and Motorola created specifically for PowerPC, are now also usable on the new Power, right? I ask because I remember that when PowerPc was born from Power, it eliminated some instructions from Power, which they said at the time were useless for the home desktop environment and instead inserted instructions made specifically for Power PC in its place ... Another curiosity that I I ask is related to floating point computation units such as the VSX and the like, deriving from the legendary Altivec. Because some people say, for example I have read some of these comments on Phoronix, that the floating point compute units of the Power processors are poor compared especially to the X86 equivalents! I wonder is such a thing ever possible when it was PowerPC's Altivec at the time, he taught Intel how to make floating point computing units, much less performing up to the SS2 version ... I don't explain this what, indeed, should be one of Power's greatest strengths, especially with the evolution that certainly all these units have had over the years ...

[ClassicHasClass]

Almost all, but not every single instruction, of the PowerPC instruction set is in Power ISA. Obviously 601-specific instructions didn't make it past the 603, but also a couple oddballs like mcrxr aren't in Power ISA (instead there is, more recently, mcrxrx), and there are differences in cache line which affects some instructions like dcbz. These were also issues on the G5, which is more POWER4 than it is PowerPC. In general, however, the vast majority of user-level code will translate to the extent it is 64-bit aware.

[MauryG5]

I understand, so we have a good part of those instructions available, certainly those 601s would not even make sense to date, I think they are too dated by now and that's right in the end. The article I read a few years ago was correct so fine. What about floating point vector and compute units instead, has Intel really outdone us in this area or are we still the best with Alti Vec's direct successors?

[ClassicHasClass]

Vectors are still "limited" to 128 bit, though I would also argue that the efficiency improvements with 256 and 512 bit vectors are more questionable. A good scalar system is what Power ISA needed, and VSX is a big improvement (no more spilling to memory to exchange between FP registers and integer registers, for example). I use it heavily in the Firefox JIT.

[MauryG5]

Understood, so you think that basically it is not really an advantage that of X86 that has vectors at 256 or 512 from what I understand ... Do you think we will be able in the end to have Firefox without those limits that up to now this Browser has on Power also compared to Chromium? I see that unfortunately I still can't go to all the sites like I do on Chromium ... I think it would be nice, given the work you do with so much passion on Firefox, to be able to finally package a version specially dedicated to us of Power, maybe diversifying some colors of the logo, for example instead of orange, use the fire red which in my opinion would represent a Power version well ...

[ClassicHasClass]

I don't really want to be in the business of making a Power-specific Firefox long term (I did that for over a decade with TenFourFox and it's a pain); I'd rather have a build that distros can pick up. The aim with the JIT is to do just that. There will necessarily be a separate branch for a bit while the code stabilizes but the goal is not to have a fork.

[MauryG5]

Yes, I understand what you mean, I made this hypothesis only to favor our build as much as possible, if it were specific it would have all the code optimized for us and would have even better performance but maybe already for how you are working, equally the final result is that of the version optimized for us. Instead as soon as possible, I need your advice since Firefox knows it better than anyone else in here perhaps, for an annoying problem that I can't solve and that afflicts the Ubuntu version and that no one has solved until now ... If you tell me where to write then to expose the problem you will be grateful ... Thanks

[ClassicHasClass]

Well, what's the exact problem? You can certainly post a report on Bugzilla but they'd probably appreciate it being triaged first.

[amock]

Are you talking about the problem reported at https://bugzilla.mozilla.org/show_bug.cgi?id=1591164?  I never got around to reopening that bug, but if you are having that problem I think that's a good place to start.  I have been building my own Firefox to get around it, but I just tested with the system Firefox and it still happens.

[MauryG5]

No I'm talking about the problem that I had already exposed some time ago on the anomalies related to Ubuntu on Power.  Whenever you open Firefox on Ubuntu, it always tells you that the history is not working because there is some other part of Ubuntu that is using that file that Firefox needs to make the history work properly.  This thing has never been solved and the bad thing is that this problem only has Firefox on Ubuntu, in other distributions including Debian, it does not happen ... I tried to delete that file that Firefox recommends me to delete in the guide but unfortunately it continues to always do it ...

[ClassicHasClass]

I think that's the same bug. I don't encounter it on Fedora. Maybe it's Ubuntu-specific.

[MauryG5]

Yes Classic, the problem is specific to the Ubuntu version, it seems that the security software that Ubuntu uses is in conflict with the Firefox bookmark and even trying to disable this Ubuntu security software, it still does not work the same ...