linux-kernel - Re: [PATCH 1/2] x86: reimplement ___preempt

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Date:	Thu, 4 Sep 2014 17:37:01 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>, X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] x86: reimplement ___preempt_schedule*() using THUNK helpers

On Thu, Sep 4, 2014 at 6:42 AM, Oleg Nesterov <oleg@...hat.com> wrote:
>
> ___preempt_schedule() does SAVE_ALL/RESTORE_ALL but this is suboptimal,
> we do not need to save/restore the callee-saved register. And we already
> have arch/x86/lib/thunk_*.S which implements the similar asm wrappers,
> so it makes sense to redefine ___preempt_schedule() as "THUNK ..." and
> remove preempt.S altogether.

Reviewed-by: Andy Lutomirski <luto@...capital.net>

>
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> ---
>  arch/x86/kernel/Makefile  |    2 --
>  arch/x86/kernel/preempt.S |   25 -------------------------
>  arch/x86/lib/thunk_32.S   |   20 ++++++++++++++++----
>  arch/x86/lib/thunk_64.S   |    7 +++++++
>  4 files changed, 23 insertions(+), 31 deletions(-)
>  delete mode 100644 arch/x86/kernel/preempt.S
>
> diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
> index b5ea75c..58cf60b 100644
> --- a/arch/x86/kernel/Makefile
> +++ b/arch/x86/kernel/Makefile
> @@ -39,8 +39,6 @@ obj-y                 += tsc.o tsc_msr.o io_delay.o rtc.o
>  obj-y                  += pci-iommu_table.o
>  obj-y                  += resource.o
>
> -obj-$(CONFIG_PREEMPT)  += preempt.o
> -
>  obj-y                          += process.o
>  obj-y                          += i387.o xsave.o
>  obj-y                          += ptrace.o
> diff --git a/arch/x86/kernel/preempt.S b/arch/x86/kernel/preempt.S
> deleted file mode 100644
> index ca7f0d5..0000000
> --- a/arch/x86/kernel/preempt.S
> +++ /dev/null
> @@ -1,25 +0,0 @@
> -
> -#include <linux/linkage.h>
> -#include <asm/dwarf2.h>
> -#include <asm/asm.h>
> -#include <asm/calling.h>
> -
> -ENTRY(___preempt_schedule)
> -       CFI_STARTPROC
> -       SAVE_ALL
> -       call preempt_schedule
> -       RESTORE_ALL
> -       ret
> -       CFI_ENDPROC
> -
> -#ifdef CONFIG_CONTEXT_TRACKING
> -
> -ENTRY(___preempt_schedule_context)
> -       CFI_STARTPROC
> -       SAVE_ALL
> -       call preempt_schedule_context
> -       RESTORE_ALL
> -       ret
> -       CFI_ENDPROC
> -
> -#endif
> diff --git a/arch/x86/lib/thunk_32.S b/arch/x86/lib/thunk_32.S
> index 28f85c9..7f1641a 100644
> --- a/arch/x86/lib/thunk_32.S
> +++ b/arch/x86/lib/thunk_32.S
> @@ -7,16 +7,19 @@
>         #include <linux/linkage.h>
>         #include <asm/asm.h>
>
> -#ifdef CONFIG_TRACE_IRQFLAGS
>         /* put return address in eax (arg1) */
> -       .macro thunk_ra name,func
> +       .macro thunk_ra name, func, put_ret_addr_in_eax=0
>         .globl \name
>  \name:
>         pushl %eax
>         pushl %ecx
>         pushl %edx
> +
> +       .if \put_ret_addr_in_eax
>         /* Place EIP in the arg1 */
>         movl 3*4(%esp), %eax
> +       .endif
> +
>         call \func
>         popl %edx
>         popl %ecx
> @@ -25,6 +28,15 @@
>         _ASM_NOKPROBE(\name)
>         .endm
>
> -       thunk_ra trace_hardirqs_on_thunk,trace_hardirqs_on_caller
> -       thunk_ra trace_hardirqs_off_thunk,trace_hardirqs_off_caller
> +#ifdef CONFIG_TRACE_IRQFLAGS
> +       thunk_ra trace_hardirqs_on_thunk,trace_hardirqs_on_caller,1
> +       thunk_ra trace_hardirqs_off_thunk,trace_hardirqs_off_caller,1
> +#endif
> +
> +#ifdef CONFIG_PREEMPT
> +       THUNK ___preempt_schedule, preempt_schedule
> +#ifdef CONFIG_CONTEXT_TRACKING
> +       THUNK ___preempt_schedule_context, preempt_schedule_context
>  #endif
> +#endif
> +
> diff --git a/arch/x86/lib/thunk_64.S b/arch/x86/lib/thunk_64.S
> index 92d9fea..b30b5eb 100644
> --- a/arch/x86/lib/thunk_64.S
> +++ b/arch/x86/lib/thunk_64.S
> @@ -38,6 +38,13 @@
>         THUNK lockdep_sys_exit_thunk,lockdep_sys_exit
>  #endif
>
> +#ifdef CONFIG_PREEMPT
> +       THUNK ___preempt_schedule, preempt_schedule
> +#ifdef CONFIG_CONTEXT_TRACKING
> +       THUNK ___preempt_schedule_context, preempt_schedule_context
> +#endif
> +#endif
> +
>         /* SAVE_ARGS below is used only for the .cfi directives it contains. */
>         CFI_STARTPROC
>         SAVE_ARGS
> --
> 1.5.5.1
>
>



-- 
Andy Lutomirski
AMA Capital Management, LLC
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