From: Nicholas Piggin <npiggin@gmail.com>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Christophe Leroy <christophe.leroy@csgroup.eu>,
Michael Ellerman <mpe@ellerman.id.au>,
msuchanek@suse.de, Paul Mackerras <paulus@samba.org>
Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v5 16/22] powerpc/syscall: Avoid stack frame in likely part of system_call_exception()
Date: Wed, 10 Feb 2021 11:56:28 +1000 [thread overview]
Message-ID: <1612921956.st2b8xlrew.astroid@bobo.none> (raw)
In-Reply-To: <f2b17529-e1b6-3d2c-a38b-51e91841e438@csgroup.eu>
Excerpts from Christophe Leroy's message of February 10, 2021 2:13 am:
>
>
> Le 09/02/2021 à 02:55, Nicholas Piggin a écrit :
>> Excerpts from Christophe Leroy's message of February 9, 2021 1:10 am:
>>> When r3 is not modified, reload it from regs->orig_r3 to free
>>> volatile registers. This avoids a stack frame for the likely part
>>> of system_call_exception()
>>
>> This doesn't on my 64s build, but it does reduce one non volatile
>> register save/restore. With quite a bit more register pressure
>> reduction 64s can avoid the stack frame as well.
>
> The stack frame is not due to the registers because on PPC64 you have the redzone that you don't
> have on PPC32.
>
> As far as I can see, this is due to a call to .arch_local_irq_restore().
>
> On ppc32 arch_local_irq_restore() is just a write to MSR.
Oh you're right there. We can actually inline fast paths of that I have
a patch somewhere, but not sure if it's worthwhile.
>> It's a cool trick but quite code and compiler specific so I don't know
>> how worthwhile it is to keep considering we're calling out into random
>> kernel C code after this.
>>
>> Maybe just keep it PPC32 specific for the moment, will have to do more
>> tuning for 64 and we have other stuff to do there first.
>>
>> If you are happy to make it 32-bit only then
>
> I think we can leave without this, that's only one or two cycles won.
Okay for this round let's drop it for now.
Thanks,
Nick
WARNING: multiple messages have this Message-ID (diff)
From: Nicholas Piggin <npiggin@gmail.com>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Christophe Leroy <christophe.leroy@csgroup.eu>,
Michael Ellerman <mpe@ellerman.id.au>,
msuchanek@suse.de, Paul Mackerras <paulus@samba.org>
Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5 16/22] powerpc/syscall: Avoid stack frame in likely part of system_call_exception()
Date: Wed, 10 Feb 2021 11:56:28 +1000 [thread overview]
Message-ID: <1612921956.st2b8xlrew.astroid@bobo.none> (raw)
In-Reply-To: <f2b17529-e1b6-3d2c-a38b-51e91841e438@csgroup.eu>
Excerpts from Christophe Leroy's message of February 10, 2021 2:13 am:
>
>
> Le 09/02/2021 à 02:55, Nicholas Piggin a écrit :
>> Excerpts from Christophe Leroy's message of February 9, 2021 1:10 am:
>>> When r3 is not modified, reload it from regs->orig_r3 to free
>>> volatile registers. This avoids a stack frame for the likely part
>>> of system_call_exception()
>>
>> This doesn't on my 64s build, but it does reduce one non volatile
>> register save/restore. With quite a bit more register pressure
>> reduction 64s can avoid the stack frame as well.
>
> The stack frame is not due to the registers because on PPC64 you have the redzone that you don't
> have on PPC32.
>
> As far as I can see, this is due to a call to .arch_local_irq_restore().
>
> On ppc32 arch_local_irq_restore() is just a write to MSR.
Oh you're right there. We can actually inline fast paths of that I have
a patch somewhere, but not sure if it's worthwhile.
>> It's a cool trick but quite code and compiler specific so I don't know
>> how worthwhile it is to keep considering we're calling out into random
>> kernel C code after this.
>>
>> Maybe just keep it PPC32 specific for the moment, will have to do more
>> tuning for 64 and we have other stuff to do there first.
>>
>> If you are happy to make it 32-bit only then
>
> I think we can leave without this, that's only one or two cycles won.
Okay for this round let's drop it for now.
Thanks,
Nick
next prev parent reply other threads:[~2021-02-10 2:27 UTC|newest]
Thread overview: 118+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-08 15:10 [PATCH v5 00/22] powerpc/32: Implement C syscall entry/exit Christophe Leroy
2021-02-08 15:10 ` Christophe Leroy
2021-02-08 15:10 ` [PATCH v5 01/22] powerpc/32s: Add missing call to kuep_lock on syscall entry Christophe Leroy
2021-02-08 15:10 ` Christophe Leroy
2021-02-08 15:10 ` [PATCH v5 02/22] powerpc/32: Always enable data translation " Christophe Leroy
2021-02-08 15:10 ` Christophe Leroy
2021-02-08 15:10 ` [PATCH v5 03/22] powerpc/32: On syscall entry, enable instruction translation at the same time as data Christophe Leroy
2021-02-08 15:10 ` Christophe Leroy
2021-02-08 15:10 ` [PATCH v5 04/22] powerpc/32: Reorder instructions to avoid using CTR in syscall entry Christophe Leroy
2021-02-08 15:10 ` Christophe Leroy
2021-02-08 15:10 ` [PATCH v5 05/22] powerpc/irq: Add helper to set regs->softe Christophe Leroy
2021-02-08 15:10 ` Christophe Leroy
2021-02-09 1:11 ` Nicholas Piggin
2021-02-09 1:11 ` Nicholas Piggin
2021-02-09 5:57 ` Christophe Leroy
2021-02-09 5:57 ` Christophe Leroy
2021-02-09 7:47 ` Nicholas Piggin
2021-02-09 7:47 ` Nicholas Piggin
2021-02-09 6:18 ` Christophe Leroy
2021-02-09 6:18 ` Christophe Leroy
2021-02-09 7:49 ` Nicholas Piggin
2021-02-09 7:49 ` Nicholas Piggin
2021-03-05 8:54 ` Christophe Leroy
2021-03-05 8:54 ` Christophe Leroy
2021-03-08 8:47 ` Nicholas Piggin
2021-03-08 8:47 ` Nicholas Piggin
2021-02-08 15:10 ` [PATCH v5 06/22] powerpc/irq: Rework helpers that manipulate MSR[EE/RI] Christophe Leroy
2021-02-08 15:10 ` Christophe Leroy
2021-02-09 1:14 ` Nicholas Piggin
2021-02-09 1:14 ` Nicholas Piggin
2021-02-08 15:10 ` [PATCH v5 07/22] powerpc/irq: Add stub irq_soft_mask_return() for PPC32 Christophe Leroy
2021-02-08 15:10 ` Christophe Leroy
2021-02-09 1:19 ` Nicholas Piggin
2021-02-09 1:19 ` Nicholas Piggin
2021-02-08 15:10 ` [PATCH v5 08/22] powerpc/syscall: Rename syscall_64.c into interrupt.c Christophe Leroy
2021-02-08 15:10 ` Christophe Leroy
2021-02-09 1:19 ` Nicholas Piggin
2021-02-09 1:19 ` Nicholas Piggin
2021-02-08 15:10 ` [PATCH v5 09/22] powerpc/syscall: Make interrupt.c buildable on PPC32 Christophe Leroy
2021-02-08 15:10 ` Christophe Leroy
2021-02-09 1:27 ` Nicholas Piggin
2021-02-09 1:27 ` Nicholas Piggin
2021-02-09 6:02 ` Christophe Leroy
2021-02-09 6:02 ` Christophe Leroy
2021-02-09 7:50 ` Nicholas Piggin
2021-02-09 7:50 ` Nicholas Piggin
2021-02-08 15:10 ` [PATCH v5 10/22] powerpc/syscall: Use is_compat_task() Christophe Leroy
2021-02-08 15:10 ` Christophe Leroy
2021-02-09 1:29 ` Nicholas Piggin
2021-02-09 1:29 ` Nicholas Piggin
2021-02-08 15:10 ` [PATCH v5 11/22] powerpc/syscall: Save r3 in regs->orig_r3 Christophe Leroy
2021-02-08 15:10 ` Christophe Leroy
2021-02-09 1:29 ` Nicholas Piggin
2021-02-09 1:29 ` Nicholas Piggin
2021-02-08 15:10 ` [PATCH v5 12/22] powerpc/syscall: Change condition to check MSR_RI Christophe Leroy
2021-02-08 15:10 ` Christophe Leroy
2021-02-09 1:36 ` Nicholas Piggin
2021-02-09 1:36 ` Nicholas Piggin
2021-02-08 15:10 ` [PATCH v5 13/22] powerpc/32: Always save non volatile GPRs at syscall entry Christophe Leroy
2021-02-08 15:10 ` Christophe Leroy
2021-02-08 15:10 ` [PATCH v5 14/22] powerpc/syscall: implement system call entry/exit logic in C for PPC32 Christophe Leroy
2021-02-08 15:10 ` Christophe Leroy
2021-02-08 15:10 ` [PATCH v5 15/22] powerpc/32: Remove verification of MSR_PR on syscall in the ASM entry Christophe Leroy
2021-02-08 15:10 ` Christophe Leroy
2021-02-08 15:10 ` [PATCH v5 16/22] powerpc/syscall: Avoid stack frame in likely part of system_call_exception() Christophe Leroy
2021-02-08 15:10 ` Christophe Leroy
2021-02-09 1:55 ` Nicholas Piggin
2021-02-09 1:55 ` Nicholas Piggin
2021-02-09 16:13 ` Christophe Leroy
2021-02-09 16:13 ` Christophe Leroy
2021-02-10 1:56 ` Nicholas Piggin [this message]
2021-02-10 1:56 ` Nicholas Piggin
2021-02-08 15:10 ` [PATCH v5 17/22] powerpc/syscall: Do not check unsupported scv vector on PPC32 Christophe Leroy
2021-02-08 15:10 ` Christophe Leroy
2021-02-09 2:00 ` Nicholas Piggin
2021-02-09 2:00 ` Nicholas Piggin
2021-02-09 6:13 ` Christophe Leroy
2021-02-09 6:13 ` Christophe Leroy
2021-02-09 7:56 ` Nicholas Piggin
2021-02-09 7:56 ` Nicholas Piggin
2021-02-08 15:10 ` [PATCH v5 18/22] powerpc/syscall: Remove FULL_REGS verification in system_call_exception Christophe Leroy
2021-02-08 15:10 ` Christophe Leroy
2021-02-09 2:02 ` Nicholas Piggin
2021-02-09 2:02 ` Nicholas Piggin
2021-02-09 14:31 ` Christophe Leroy
2021-02-09 14:31 ` Christophe Leroy
2021-02-10 1:57 ` Nicholas Piggin
2021-02-10 1:57 ` Nicholas Piggin
2021-02-08 15:10 ` [PATCH v5 19/22] powerpc/syscall: Optimise checks in beginning of system_call_exception() Christophe Leroy
2021-02-08 15:10 ` Christophe Leroy
2021-02-09 2:06 ` Nicholas Piggin
2021-02-09 2:06 ` Nicholas Piggin
2021-02-09 14:32 ` Christophe Leroy
2021-02-09 14:32 ` Christophe Leroy
2021-02-08 15:10 ` [PATCH v5 20/22] powerpc/syscall: Avoid storing 'current' in another pointer Christophe Leroy
2021-02-08 15:10 ` Christophe Leroy
2021-02-09 2:36 ` Nicholas Piggin
2021-02-09 2:36 ` Nicholas Piggin
2021-02-09 13:50 ` Segher Boessenkool
2021-02-09 13:50 ` Segher Boessenkool
2021-02-09 14:31 ` David Laight
2021-02-09 14:31 ` David Laight
2021-02-09 17:03 ` Christophe Leroy
2021-02-09 17:03 ` Christophe Leroy
2021-02-09 17:16 ` David Laight
2021-02-09 17:16 ` David Laight
2021-02-10 2:00 ` Nicholas Piggin
2021-02-10 2:00 ` Nicholas Piggin
2021-02-10 8:45 ` Christophe Leroy
2021-02-10 8:45 ` Christophe Leroy
2021-02-08 15:10 ` [PATCH v5 21/22] powerpc/32: Remove the counter in global_dbcr0 Christophe Leroy
2021-02-08 15:10 ` Christophe Leroy
2021-02-08 15:10 ` [PATCH v5 22/22] powerpc/32: Handle bookE debugging in C in syscall entry/exit Christophe Leroy
2021-02-08 15:10 ` Christophe Leroy
2021-02-09 1:03 ` [PATCH v5 00/22] powerpc/32: Implement C " Nicholas Piggin
2021-02-09 1:03 ` Nicholas Piggin
2021-02-12 0:19 ` Michael Ellerman
2021-02-12 0:19 ` Michael Ellerman
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