FWIW, my understanding is that XBEGIN/XEND/XABORT are still available on the affected CPUs. Only XACQUIRE/XRELEASE are disabled. So the clock isn't really reset.
I, too, wish TSX was more ubiquitous. I'm working on a kernel, and was hoping to use TSX to greatly simplify the logic of safely reading user memory from kernelspace - catching various exception cases without going through the real exception handler.
Turns out, none of the machines I have at my disposal have TSX - not my Desktop PC nor my server machine. So, RIP that plan, I guess.
What you want is absolutely doable with TSX. The overhead might be significant though. I wouldn't be surprised if locking a mutex was faster.
You can’t simplify the logic because TSX transactions may abort for any reason and make no promises of forward progress. You must implement a fallback codepath.
If you meant having an optimized codepath then that is doable. But given your writing a kernel there may be microarchitectural hazards that trigger excessive aborts.
Forget microarchitectural issues. If you have user memory paged out (or not present for accounting reasons, etc), you can try to access it in a transaction until the cows come home and it will never work — to make progress, you need to update the page tables either via a page fault or manually.
Not an issue for me, my kernel has no swap or other such thing - by design. Of course I realize not everyone is in my shoes - such an approach would absolutely fail on Linux!
In some cases it can have a huge speedup. But it's rather tricky to get right. So far for almost all of my use cases the transaction sizes have been too large, and it almost always aborted.
The RPCS3 PS 3 emulator saw a 40% perf boost so some amazing gains are possible.
I, too, wish TSX was more ubiquitous. I'm working on a kernel, and was hoping to use TSX to greatly simplify the logic of safely reading user memory from kernelspace - catching various exception cases without going through the real exception handler.
Turns out, none of the machines I have at my disposal have TSX - not my Desktop PC nor my server machine. So, RIP that plan, I guess.
What you want is absolutely doable with TSX. The overhead might be significant though. I wouldn't be surprised if locking a mutex was faster.