From: Nicholas Piggin <npiggin@gmail.com>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Christophe Leroy <christophe.leroy@c-s.fr>,
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: [RFC PATCH v2 12/13] powerpc/kernel: Do not inconditionally save non volatile registers on system call
Date: Tue, 07 Apr 2020 10:26:58 +1000 [thread overview]
Message-ID: <1586218971.lolwg4f0lh.astroid@bobo.none> (raw)
In-Reply-To: <48d3e2e5-318f-011e-a59b-ec89bd7b76d2@c-s.fr>
Christophe Leroy's on April 7, 2020 4:18 am:
>
>
> Le 06/04/2020 à 03:25, Nicholas Piggin a écrit :
>> Christophe Leroy's on April 6, 2020 3:44 am:
>>> Before : 347 cycles on null_syscall
>>> After : 327 cycles on null_syscall
>>
>> The problem I had doing this is that signal delivery wnats full regs,
>> and you don't know if you have a signal pending ahead of time if you
>> have interrupts enabled.
>>
>> I began to try bailing out back to asm to save nvgprs and call again.
>> I think that can be made to work, but it is more complication in asm,
>> and I soon found that 64s CPUs don't care about NVGPRs too much so it's
>> nice to get rid of the !fullregs state.
>
> I tried a new way in v3, please have a look. I split
> syscall_exit_prepare() in 3 parts and the result is unexpected: it is
> better than before the series (307 cycles now versus 311 cycles with
> full ASM syscall entry/exit).
Great! Well I don't really see a problem with how you changed the C code
around. I'll have to look at the assembly but I don't think it would
have caused a problem for 64s.
Thanks,
Nick
next prev parent reply other threads:[~2020-04-07 0:28 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-05 17:44 [RFC PATCH v2 01/13] powerpc/radix: Make kuap_check_amr() and kuap_restore_amr() generic Christophe Leroy
2020-04-05 17:44 ` [RFC PATCH v2 02/13] powerpc/32s: Create C version of kuap_restore() and kuap_check() Christophe Leroy
2020-04-05 17:44 ` [RFC PATCH v2 03/13] powerpc/8xx: " Christophe Leroy
2020-04-05 17:44 ` [RFC PATCH v2 04/13] powerpc/irq: Add new helpers to play with MSR_EE and MSR_RI on PPC32 Christophe Leroy
2020-04-05 17:44 ` [RFC PATCH v2 05/13] powerpc/syscall: Rename syscall_64.c into syscall.c Christophe Leroy
2020-04-06 1:42 ` Nicholas Piggin
2020-04-06 18:20 ` Christophe Leroy
2020-04-07 0:22 ` Nicholas Piggin
2020-04-05 17:44 ` [RFC PATCH v2 06/13] powerpc/syscall: Make syscall_64.c buildable on PPC32 Christophe Leroy
2020-04-06 1:52 ` Nicholas Piggin
2020-04-06 18:21 ` Christophe Leroy
2020-04-05 17:44 ` [RFC PATCH v2 07/13] powerpc/syscall: Use is_compat_task() Christophe Leroy
2020-04-05 17:44 ` [RFC PATCH v2 08/13] powerpc/syscall: Save r3 in regs->orig_r3 Christophe Leroy
2020-04-05 17:44 ` [RFC PATCH v2 09/13] powerpc/syscall: Selectively check MSR_RI and MSR_PR on syscall entry Christophe Leroy
2020-04-05 17:44 ` [RFC PATCH v2 10/13] powerpc/syscall: system call implement entry/exit logic in C for PPC32 Christophe Leroy
2020-04-05 17:44 ` [RFC PATCH v2 11/13] powerpc/syscall: Avoid stack frame in likely part of syscall_call_exception() Christophe Leroy
2020-04-06 1:29 ` Nicholas Piggin
2020-04-06 18:19 ` Christophe Leroy
2020-04-05 17:44 ` [RFC PATCH v2 12/13] powerpc/kernel: Do not inconditionally save non volatile registers on system call Christophe Leroy
2020-04-06 1:25 ` Nicholas Piggin
2020-04-06 18:18 ` Christophe Leroy
2020-04-07 0:26 ` Nicholas Piggin [this message]
2020-04-05 17:44 ` [RFC PATCH v2 13/13] powerpc/kernel: Do not use READ_ONCE() to access current thread_info flags Christophe Leroy
2020-04-06 1:39 ` Nicholas Piggin
2020-04-06 1:40 ` [RFC PATCH v2 01/13] powerpc/radix: Make kuap_check_amr() and kuap_restore_amr() generic Nicholas Piggin
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