On Wed, Mar 18, 2015 at 04:52:14PM +0000, Mathieu Desnoyers wrote: > ----- Original Message ----- > > On Wed, Mar 18, 2015 at 12:23:02PM -0400, Mathieu Desnoyers wrote: > > > memory barriers in reader: 1701557485 reads, 3129842 writes > > > signal-based scheme: 9825306874 reads, 5386 writes > > > sys_membarrier: 7992076602 reads, 220 writes > > > > > > The dynamic sys_membarrier availability check adds some overhead to > > > the read-side compared to the signal-based scheme, but besides that, > > > with the expedited scheme, we can see that we are close to the read-side > > > performance of the signal-based scheme. However, this non-expedited > > > sys_membarrier implementation has a much slower grace period than signal > > > and memory barrier schemes. > > > > Doesn't the query flag allow you to find out in advance rather than > > dynamically within the reader? What's the reader performance if you > > hardcode availability of membarrier? > > What I am currently doing is to use sys_membarrier with a query > flag within a lib constructor, and cache the result in a global > variable. In the reader, I just test the variable, and thus detect > whether I can use sys_membarrier, or if I need to fallback to > barriers on both reader and writer. > > Are you suggesting I try removing the global variable load+test > from the reader fast path ?
Right. You said that "The dynamic sys_membarrier availability check adds some overhead to the read-side compared to the signal-based scheme"; I wondered how much. - Josh Triplett -- 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/
