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Subject: Re: [RFC PATCH 0/9] powerpc/64s: fast interrupt exit
To: Nicholas Piggin <npiggin@gmail.com>, linuxppc-dev@lists.ozlabs.org
References: <20201106155929.2246055-1-npiggin@gmail.com>
From: Christophe Leroy <christophe.leroy@csgroup.eu>
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Date: Sat, 7 Nov 2020 11:35:11 +0100
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Le 06/11/2020 à 16:59, Nicholas Piggin a écrit :
> This series attempts to improve the speed of interrupts and system calls
> in two major ways.
> 
> Firstly, the SRR/HSRR registers do not need to be reloaded if they were
> not used or clobbered fur the duration of the interrupt.
> 
> Secondly, an alternate return location facility is added for soft-masked
> asynchronous interrupts and then that's used to set everything up for
> return without having to disable MSR RI or EE.
> 
> After this series, the entire system call / interrupt handler fast path
> executes no mtsprs and one mtmsrd to enable interrupts initially, and
> the system call vectored path doesn't even need to do that.

Interesting series.

Unfortunately, can't be done on PPC32 (at least on non bookE), because it would mean mapping kernel 
at 0 instead of 0xC0000000. Not sure libc would like it, and anyway it would be an issue for 
catching NULL pointer dereferencing, unless we use page tables instead of BATs to map kernel mem, 
which would be serious performance cut.

Christophe

> 
> Thanks,
> Nick
> 
> Nicholas Piggin (9):
>    powerpc/64s: syscall real mode entry use mtmsrd rather than rfid
>    powerpc/64s: system call avoid setting MSR[RI] until we set MSR[EE]
>    powerpc/64s: introduce different functions to return from SRR vs HSRR
>      interrupts
>    powerpc/64s: avoid reloading (H)SRR registers if they are still valid
>    powerpc/64: move interrupt return asm to interrupt_64.S
>    powerpc/64s: save one more register in the masked interrupt handler
>    powerpc/64s: allow alternate return locations for soft-masked
>      interrupts
>    powerpc/64s: interrupt soft-enable race fix
>    powerpc/64s: use interrupt restart table to speed up return from
>      interrupt
> 
>   arch/powerpc/Kconfig.debug                 |   5 +
>   arch/powerpc/include/asm/asm-prototypes.h  |   4 +-
>   arch/powerpc/include/asm/head-64.h         |   2 +-
>   arch/powerpc/include/asm/interrupt.h       |  18 +
>   arch/powerpc/include/asm/paca.h            |   3 +
>   arch/powerpc/include/asm/ppc_asm.h         |   8 +
>   arch/powerpc/include/asm/ptrace.h          |  28 +-
>   arch/powerpc/kernel/asm-offsets.c          |   5 +
>   arch/powerpc/kernel/entry_64.S             | 508 ---------------
>   arch/powerpc/kernel/exceptions-64s.S       | 180 ++++--
>   arch/powerpc/kernel/fpu.S                  |   2 +
>   arch/powerpc/kernel/head_64.S              |   5 +-
>   arch/powerpc/kernel/interrupt_64.S         | 720 +++++++++++++++++++++
>   arch/powerpc/kernel/irq.c                  |  79 ++-
>   arch/powerpc/kernel/kgdb.c                 |   2 +-
>   arch/powerpc/kernel/kprobes-ftrace.c       |   2 +-
>   arch/powerpc/kernel/kprobes.c              |  10 +-
>   arch/powerpc/kernel/process.c              |  21 +-
>   arch/powerpc/kernel/rtas.c                 |  13 +-
>   arch/powerpc/kernel/signal.c               |   2 +-
>   arch/powerpc/kernel/signal_64.c            |  14 +
>   arch/powerpc/kernel/syscall_64.c           | 242 ++++---
>   arch/powerpc/kernel/syscalls.c             |   2 +
>   arch/powerpc/kernel/traps.c                |  18 +-
>   arch/powerpc/kernel/vector.S               |   6 +-
>   arch/powerpc/kernel/vmlinux.lds.S          |  10 +
>   arch/powerpc/lib/Makefile                  |   2 +-
>   arch/powerpc/lib/restart_table.c           |  26 +
>   arch/powerpc/lib/sstep.c                   |   5 +-
>   arch/powerpc/math-emu/math.c               |   2 +-
>   arch/powerpc/mm/fault.c                    |   2 +-
>   arch/powerpc/perf/core-book3s.c            |  19 +-
>   arch/powerpc/platforms/powernv/opal-call.c |   3 +
>   arch/powerpc/sysdev/fsl_pci.c              |   2 +-
>   34 files changed, 1244 insertions(+), 726 deletions(-)
>   create mode 100644 arch/powerpc/kernel/interrupt_64.S
>   create mode 100644 arch/powerpc/lib/restart_table.c
>