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: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH v2 12/13] powerpc/kernel: Do not inconditionally save non volatile registers on system call
Date: Mon, 06 Apr 2020 11:25:20 +1000 [thread overview]
Message-ID: <1586135554.pnqaj0giue.astroid@bobo.none> (raw)
In-Reply-To: <4ef6d617cfd34e09e9bf5a456b2e0b6d2a8a3c96.1586108649.git.christophe.leroy@c-s.fr>
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.
Possibly another approach would be to leave interrupts disabled for the
case where you have no work to do. You could create a small
syscall_exit_prepare_nowork fastpath for that case for 32-bit, perhaps?
Thanks,
Nick
next prev parent reply other threads:[~2020-04-06 1:28 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 [this message]
2020-04-06 18:18 ` Christophe Leroy
2020-04-07 0:26 ` Nicholas Piggin
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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