Messages in this thread | | | Subject | Re: [RFC WIP PATCH] powerpc/32: system call implement entry/exit logic in C | From | Christophe Leroy <> | Date | Sun, 5 Apr 2020 20:53:00 +0200 |
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Le 03/04/2020 à 09:33, Nicholas Piggin a écrit : > Christophe Leroy's on April 1, 2020 9:48 pm: >> >> >> Le 31/03/2020 à 17:22, Christophe Leroy a écrit : >>> That's first try to port PPC64 syscall entry/exit logic in C to PPC32. >>> I've do the minimum to get it work. I have not reworked calls >>> to sys_fork() and friends for instance. >>> >>> For the time being, it seems to work more or less but: >>> - ping reports EINVAL on recvfrom >>> - strace shows NULL instead of strings in call like open() for instance. >> >> For the two above problems, that's because system_call_exception() >> doesn't set orig_gpr3 whereas DoSycall() does in entry_32.S . Is that >> only done on PPC32 ? >> >> With the following line at the begining of system_call_exception(), it >> works perfectly: >> >> regs->orig_gpr3 = r3; > > Oh great, nice work. We should be able to make some simple helpers or > move some things a bit to reduce the amount of ifdefs in the C code. > It doesn't look too bad though. > >> I will now focus on performance to see if we can do something about it. > > What's the performance difference between current asm code just with > always saving NVGPRS vs C?
Done new measurement and sent a series. lower values now because the time accounting was done twice as it was still in the ASM part.
Before the series, 311 cycles for a null_syscall If adding SAVE_NVGPRS to the entry macro, 335 cycles
First patch: 353 cycles ie +13,5%
After a few changes, including conditional saving of non volatile registers, I get 325 cycles that is only +4,5%. I thing that's acceptable.
Do you see a problem with still saving non volatile registers only when required ?
Christophe
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