Re: [RFC PATCH v2 2/3] thread_local_abi: wire up x86 32/64 system call

[Josh Triplett]

On December 22, 2015 10:02:12 AM PST, Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> wrote:
>Wire up the thread local ABI on x86 32/64. Call the
>thread_local_abi_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 x86 by removing the need to perform a function call, "lsl"
>instruction, or system call on the fast path.
>
>Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
>CC: Russell King <linux@xxxxxxxxxxxxxxxx>
>CC: Catalin Marinas <catalin.marinas@xxxxxxx>
>CC: Will Deacon <will.deacon@xxxxxxx>
>CC: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
>CC: Paul Turner <pjt@xxxxxxxxxx>
>CC: Andrew Hunter <ahh@xxxxxxxxxx>
>CC: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
>CC: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
>CC: Andi Kleen <andi@xxxxxxxxxxxxxx>
>CC: Dave Watson <davejwatson@xxxxxx>
>CC: Chris Lameter <cl@xxxxxxxxx>
>CC: Ingo Molnar <mingo@xxxxxxxxxx>
>CC: Ben Maurer <bmaurer@xxxxxx>
>CC: Steven Rostedt <rostedt@xxxxxxxxxxx>
>CC: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
>CC: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
>CC: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
>CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>CC: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
>CC: linux-api@xxxxxxxxxxxxxxx
>---
> arch/x86/entry/common.c                | 2 ++
> arch/x86/entry/syscalls/syscall_32.tbl | 1 +
> arch/x86/entry/syscalls/syscall_64.tbl | 1 +
> 3 files changed, 4 insertions(+)
>
>diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
>index a89fdbc..222cacf 100644
>--- a/arch/x86/entry/common.c
>+++ b/arch/x86/entry/common.c
>@@ -249,6 +249,8 @@ static void exit_to_usermode_loop(struct pt_regs
>*regs, u32 cached_flags)
> 		if (cached_flags & _TIF_NOTIFY_RESUME) {
> 			clear_thread_flag(TIF_NOTIFY_RESUME);
> 			tracehook_notify_resume(regs);
>+			if (thread_local_abi_active(current))
>+				thread_local_abi_handle_notify_resume(current);

Every caller seems likely to duplicate this pattern; why not make the call itself a static inline containing this check and call (or no-op if compiled out)?

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