On Fri, Jun 03, 2016 at 05:20:10PM -0400, Waiman Long wrote: > On 06/03/2016 05:48 AM, Pan Xinhui wrote: > >queued_spin_lock_slowpath should not worry about interrupt change > >node->count by accident because ->count is inc and dec when we > >enter/leave queued_spin_lock_slowpath. > > > >So this_cpu_dec() does some no point things here, lets use this_cpu_ptr > >for a small optimization. > > > >Signed-off-by: Pan Xinhui<xinhui....@linux.vnet.ibm.com> > >--- > > kernel/locking/qspinlock.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > >diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c > >index 99f31e4..2b4daac 100644 > >--- a/kernel/locking/qspinlock.c > >+++ b/kernel/locking/qspinlock.c > >@@ -492,7 +492,7 @@ release: > > /* > > * release the node > > */ > >- this_cpu_dec(mcs_nodes[0].count); > >+ this_cpu_ptr(&mcs_nodes[0])->count--; > > } > > EXPORT_SYMBOL(queued_spin_lock_slowpath); > > > > Is this going to generate better code for PPC? For x86, I think it will > cause more instruction to be issued.
It does; I think he wants __this_cpu_dec() instead, but the Changelog needs improvement to explain why that is ok.
