GCC is unable to properly optimize functions that have a very short likely case and a longer and register-heavier cold part -- it fails to sink all of the register saving and stack frame setup code into the unlikely part.
Help it out with prepare_exit_to_usermode by splitting it into two parts and inline the hot part. Saves 6-8 cycles for compat syscalls. Signed-off-by: Andy Lutomirski <[email protected]> --- arch/x86/entry/common.c | 43 ++++++++++++++++++++++++++++--------------- 1 file changed, 28 insertions(+), 15 deletions(-) diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c index 3d44c83f2769..d6b8f4fd8274 100644 --- a/arch/x86/entry/common.c +++ b/arch/x86/entry/common.c @@ -218,14 +218,12 @@ long syscall_trace_enter(struct pt_regs *regs) return syscall_trace_enter_phase2(regs, arch, phase1_result); } -/* Called with IRQs disabled. */ -__visible void prepare_exit_to_usermode(struct pt_regs *regs) -{ - if (IS_ENABLED(CONFIG_PROVE_LOCKING) && WARN_ON(!irqs_disabled())) - local_irq_disable(); - - lockdep_sys_exit(); +#define EXIT_TO_USERMODE_LOOP_FLAGS \ + (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE | \ + _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY) +static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags) +{ /* * In order to return to user mode, we need to have IRQs off with * none of _TIF_SIGPENDING, _TIF_NOTIFY_RESUME, _TIF_USER_RETURN_NOTIFY, @@ -235,14 +233,6 @@ __visible void prepare_exit_to_usermode(struct pt_regs *regs) * work to clear some of the flags can sleep. */ while (true) { - u32 cached_flags = - READ_ONCE(pt_regs_to_thread_info(regs)->flags); - - if (!(cached_flags & (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | - _TIF_UPROBE | _TIF_NEED_RESCHED | - _TIF_USER_RETURN_NOTIFY))) - break; - /* We have work to do. */ local_irq_enable(); @@ -266,7 +256,30 @@ __visible void prepare_exit_to_usermode(struct pt_regs *regs) /* Disable IRQs and retry */ local_irq_disable(); + + cached_flags = READ_ONCE(pt_regs_to_thread_info(regs)->flags); + + if (!(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS)) + break; + } +} + +/* Called with IRQs disabled. */ +__visible inline void prepare_exit_to_usermode(struct pt_regs *regs) +{ + u32 cached_flags; + + if (IS_ENABLED(CONFIG_PROVE_LOCKING) && WARN_ON(!irqs_disabled())) + local_irq_disable(); + + lockdep_sys_exit(); + + cached_flags = + READ_ONCE(pt_regs_to_thread_info(regs)->flags); + + if (unlikely(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS)) + exit_to_usermode_loop(regs, cached_flags); user_enter(); } -- 2.4.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
