2013/10/25 Peter Zijlstra <pet...@infradead.org>: > On Wed, Oct 23, 2013 at 03:19:51PM +0100, Frederic Weisbecker wrote: > I would argue for: > > READ ->data_tail READ ->data_head > smp_rmb() (A) smp_rmb() (C) > WRITE $data READ $data > smp_wmb() (B) smp_mb() (D) > STORE ->data_head WRITE ->data_tail > > Where A pairs with D, and B pairs with C. > > I don't think A needs to be a full barrier because we won't in fact > write data until we see the store from userspace. So we simply don't > issue the data WRITE until we observe it. > > OTOH, D needs to be a full barrier since it separates the data READ from > the tail WRITE. > > For B a WMB is sufficient since it separates two WRITEs, and for C an > RMB is sufficient since it separates two READs.
Hmm, I need to defer on you for that, I'm not yet comfortable with picking specific barrier flavours when both write and read are involved in a same side :) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
