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

[Mathieu Desnoyers <mathieu.desnoyers-vg+e7yoeK/dWk0Htik3J/w@public.gmane.org>]

----- On Dec 23, 2015, at 10:42 PM, Josh Triplett josh-iaAMLnmF4UmaiuxdJuQwMA@public.gmane.org wrote:

> On December 22, 2015 10:02:12 AM PST, Mathieu Desnoyers
> <mathieu.desnoyers-vg+e7yoeK/dWk0Htik3J/w@public.gmane.org> 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-vg+e7yoeK/dWk0Htik3J/w@public.gmane.org>
>>CC: Russell King <linux-lFZ/pmaqli7XmaaqVzeoHQ@public.gmane.org>
>>CC: Catalin Marinas <catalin.marinas-5wv7dgnIgG8@public.gmane.org>
>>CC: Will Deacon <will.deacon-5wv7dgnIgG8@public.gmane.org>
>>CC: Thomas Gleixner <tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>
>>CC: Paul Turner <pjt-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
>>CC: Andrew Hunter <ahh-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
>>CC: Peter Zijlstra <peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
>>CC: Andy Lutomirski <luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org>
>>CC: Andi Kleen <andi-Vw/NltI1exuRpAAqCnN02g@public.gmane.org>
>>CC: Dave Watson <davejwatson-b10kYP2dOMg@public.gmane.org>
>>CC: Chris Lameter <cl-vYTEC60ixJUAvxtiuMwx3w@public.gmane.org>
>>CC: Ingo Molnar <mingo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
>>CC: Ben Maurer <bmaurer-b10kYP2dOMg@public.gmane.org>
>>CC: Steven Rostedt <rostedt-nx8X9YLhiw1AfugRpC6u6w@public.gmane.org>
>>CC: "Paul E. McKenney" <paulmck-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>
>>CC: Josh Triplett <josh-iaAMLnmF4UmaiuxdJuQwMA@public.gmane.org>
>>CC: Linus Torvalds <torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
>>CC: Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
>>CC: Thomas Gleixner <tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>
>>CC: linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
>>---
>> 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)?

Very good point, I'll do that.

Thanks!

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com