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    Subject[RFC PATCH v2 2/3] getcpu_cache: wire up ARM system call
    Date
    Wire up the getcpu cache system call on 32-bit ARM. Call the
    getcpu_cache_handle_notify_resume() function on return to
    userspace if TIF_NOTIFY_RESUME thread flag is set.

    This provides an ABI improving the speed of a getcpu operation
    on ARM by skipping the getcpu system call on the fast path.

    Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
    CC: Russell King <linux@arm.linux.org.uk>
    CC: Catalin Marinas <catalin.marinas@arm.com>
    CC: Will Deacon <will.deacon@arm.com>
    CC: Thomas Gleixner <tglx@linutronix.de>
    CC: Paul Turner <pjt@google.com>
    CC: Andrew Hunter <ahh@google.com>
    CC: Peter Zijlstra <peterz@infradead.org>
    CC: Andy Lutomirski <luto@amacapital.net>
    CC: Andi Kleen <andi@firstfloor.org>
    CC: Dave Watson <davejwatson@fb.com>
    CC: Chris Lameter <cl@linux.com>
    CC: Ingo Molnar <mingo@redhat.com>
    CC: Ben Maurer <bmaurer@fb.com>
    CC: Steven Rostedt <rostedt@goodmis.org>
    CC: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
    CC: Josh Triplett <josh@joshtriplett.org>
    CC: Linus Torvalds <torvalds@linux-foundation.org>
    CC: Andrew Morton <akpm@linux-foundation.org>
    CC: Thomas Gleixner <tglx@linutronix.de>
    CC: linux-api@vger.kernel.org
    ---
    arch/arm/include/uapi/asm/unistd.h | 1 +
    arch/arm/kernel/calls.S | 1 +
    arch/arm/kernel/signal.c | 1 +
    3 files changed, 3 insertions(+)

    diff --git a/arch/arm/include/uapi/asm/unistd.h b/arch/arm/include/uapi/asm/unistd.h
    index ede692f..ea0ea94 100644
    --- a/arch/arm/include/uapi/asm/unistd.h
    +++ b/arch/arm/include/uapi/asm/unistd.h
    @@ -417,6 +417,7 @@
    #define __NR_userfaultfd (__NR_SYSCALL_BASE+388)
    #define __NR_membarrier (__NR_SYSCALL_BASE+389)
    #define __NR_mlock2 (__NR_SYSCALL_BASE+390)
    +#define __NR_getcpu_cache (__NR_SYSCALL_BASE+391)

    /*
    * The following SWIs are ARM private.
    diff --git a/arch/arm/kernel/calls.S b/arch/arm/kernel/calls.S
    index ac368bb..aa43e29 100644
    --- a/arch/arm/kernel/calls.S
    +++ b/arch/arm/kernel/calls.S
    @@ -400,6 +400,7 @@
    CALL(sys_userfaultfd)
    CALL(sys_membarrier)
    CALL(sys_mlock2)
    +/* 391 */ CALL(sys_getcpu_cache)
    #ifndef syscalls_counted
    .equ syscalls_padding, ((NR_syscalls + 3) & ~3) - NR_syscalls
    #define syscalls_counted
    diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c
    index 7b8f214..ff5052c 100644
    --- a/arch/arm/kernel/signal.c
    +++ b/arch/arm/kernel/signal.c
    @@ -594,6 +594,7 @@ do_work_pending(struct pt_regs *regs, unsigned int thread_flags, int syscall)
    } else {
    clear_thread_flag(TIF_NOTIFY_RESUME);
    tracehook_notify_resume(regs);
    + getcpu_cache_handle_notify_resume(current);
    }
    }
    local_irq_disable();
    --
    2.1.4
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