lkml.org 
[lkml]   [2017]   [Sep]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: Memory-ordering recipes
On Mon, Sep 18, 2017 at 07:25:48AM -0700, Paul E. McKenney wrote:
> On Mon, Sep 18, 2017 at 03:52:42PM +0800, Boqun Feng wrote:
> > On Sun, Sep 17, 2017 at 04:05:09PM -0700, Paul E. McKenney wrote:
> > > Hello!
> > >
> >
> > Hi Paul,
> >
> > > The topic of memory-ordering recipes came up at the Linux Plumbers
> > > Conference microconference on Friday, so I thought that I should summarize
> > > what is currently "out there":
> > >
> > > 1. memory-barriers.txt: A bit rambling and diffuse for a recipes
> > > document.
> > >
> > > 2. https://www.kernel.org/pub/linux/kernel/people/paulmck/LWNLinuxMM/Examples.html
> > > Many of the examples are on-point, but this is aimed more
> > > at understanding the memory model than at an organized set
> > > of recipes.
> > >
> > > 3. https://www.kernel.org/pub/linux/kernel/people/paulmck/LWNLinuxMM/Examples.html
> >
> > Duplicate links ;-) This should a link to some slides?
>
> Indeed! How about this one?
>
> http://www.linuxplumbersconf.org/2017/ocw//system/presentations/4708/original/LKMM-overview.2017.09.15b.pdf
>

Got it.

Thanks for the link ;-)

Regards,
Boqun

> > > Slides 15-20. Again, some of the litmus tests are on-point,
> > > but the focus is more on understanding the memory model than on
> > > an organized set of recipes.
> > >
> > > So what litmus tests are needed? Here is my initial set:
> > >
> > > 1. Release-acquire chains, AKA ISA2, Z6.2, LB, and 3.LB
> > >
> > > Lots of variety here, can in some cases substitute:
> > >
> > > a. READ_ONCE() for smp_load_acquire()
> > > b. WRITE_ONCE() for smp_store_release()
> > > c. Dependencies for both smp_load_acquire() and
> > > smp_store_release().
> > > d. smp_wmb() for smp_store_release() in first thread
> > > of ISA2 and Z6.2.
> > > e. smp_rmb() for smp_load_acquire() in last thread of ISA2.
> > >
> > > 2. MP (see test6.pdf for nickname translation)
> > >
> > > a. smp_store_release() / smp_load_acquire()
> > > b. rcu_assign_pointer() / rcu_dereference()
> > > c. smp_wmb() / smp_rmb()
> > > d. Replacing either of the above with smp_mb()
> > >
> > > 3. SB
> > >
> > > a. smp_mb(), as in lockless wait-wakeup coordination.
> > > And as in sys_membarrier()-scheduler coordination,
> > > for that matter.
> >
> > b. replace smp_mb() with smp_mb__before_atomic() followed
> > by a _relaxed cmpchg? As in pv_kick_node():
> >
> > https://marc.info/?l=linux-kernel&m=150274124711012
> >
> > Besides, do we also want to add Co* into the set? I think there may be
> > some people still confused to think per-loc SC is not held, and they may
> > add unnecessary barriers in their code. Those (Co*) recipes could serve
> > as a guide for state-machine style programming. Thoughts?
>
> Indeed, it would be good to have some single-variable-SC recipes.
>
> And single-variable-SC holds only if you use READ_ONCE(). ;-)
>
> Thanx, Paul
>
[unhandled content-type:application/pgp-signature]
\
 
 \ /
  Last update: 2017-09-19 04:00    [W:0.053 / U:0.316 seconds]
©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site