Question about dec_lock_cnt method in Context class
ryx at gwmail.gwu.edu
Mon Sep 1 17:04:37 CEST 2014
Thanks a lot!
I will try it.
But could you explain to me why this is better?
I am really curious about how to implement and debug such staff.
On Mon, Sep 1, 2014 at 5:58 AM, Adam Lackorzynski <adam at os.inf.tu-dresden.de
> On Fri Aug 29, 2014 at 13:46:38 -0400, Yuxin Ren wrote:
> > I have some further understanding about the code.
> > If thread A can go back to its home cpu(core 1), this means it is not
> > running on the core 2.
> > And when A release its lock, it will switch to its helper.
> > During the context switch from thread A to its helper on core 2, the "
> > _running_under_lock"
> > of thread A should be set to false. Thus thread A is able to continue to
> > run on its home cpu.
> > I think this logic has no problem. But I observed a thread going into
> > the infinite loop in Switch_lock::set_lock_owner method.
> > in my test program.
> > Because of inappropriate memory barrier, or anything else?
> > On Wed, Aug 27, 2014 at 2:28 PM, Yuxin Ren <ryx at gwmail.gwu.edu> wrote:
> > > I have a question about the dec_lock_cnt method in Context class under
> > > multiple processor.
> > > In its implementation, it checks if thread's home cpu is equal to
> > > cpu.
> > > If not, it does not unset "_running_under_lock" variable, even if the
> > > _lock_cnt is 0.
> > > Why does it check if home cpu is equal to current cpu?
> This one should work better:
> int n = _lock_cnt - 1;
> write_now(&_lock_cnt, n);
> if (EXPECT_TRUE(!n && home_cpu() == current_cpu()))
> write_now(&_running_under_lock, Mword(false));
> Adam adam at os.inf.tu-dresden.de
> Lackorzynski http://os.inf.tu-dresden.de/~adam/
> l4-hackers mailing list
> l4-hackers at os.inf.tu-dresden.de
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