Thanks for fixing it up! On Jan 18, 2011, at 6:13 PM, Samuel Thibault wrote:
> Jeff Squyres, le Tue 18 Jan 2011 20:00:42 +0100, a écrit : >> On Jan 12, 2011, at 10:10 AM, Samuel Thibault wrote: >>> This is not what I meant: hwloc_alloc_membind_policy's purpose is only >>> to allocate bound memory. It happens that hwloc_alloc_membind_policy >>> _may_ change the process policy in order to be able to bind memory >>> at all (when the underlying OS does not have a directed allocation >>> primitive), but that's not necessary. If hwloc can simply call a >>> directed allocation primitive, it will do it. If the OS doesn't support >>> binding at all, then hwloc will just allocate memory. >> >> How's this? >> >> * Setting this policy will cause the OS to try to bind a new memory >> * allocation to the specified set. > > Err, no, again hwloc_alloc_membind_policy's purpose is _not_ to set a > policy for future allocations, but _only_ to allocate data. It just > _happens_ to possibly have to change the current process policy in order > to achieve the binding, but that's only a side effect. Think of it as > "allocate bound memory, possibly changing the policy just for that". > >> As a side effect, some operating >> * systems may change the current memory binding policy; > > It's not really the system that changes the current memory binding > policy, it's hwloc which explicitly requests the operating to do so, in > order to actually get the desired binding. > > I have rephrased it. > >>>> + HWLOC_MEMBIND_INTERLEAVE = 3, /**< \brief Allocate memory on >>> >>> This is not really correct: if the threads were splitting the memory >>> amongst themselves, FIRSTTOUCH should be used instead, to migrate pages >>> close to where they are referenced from. I have rephrased that >> >> What's a good simple example scenario when it would be good to use >> INTERLEAVE, then? > > Well, this is what I have put instead: > > "Interleaving can be useful when threads distributed across the > specified NUMA nodes will all be accessing the whole memory range > concurrently, since the interleave will then balance the memory > references." > > By "the whole", I really mean _all_ the threads will access the _whole_ > range, without known separation, e.g. a coefficient vector that all > threads need to read to perform some computation. > > Samuel > _______________________________________________ > hwloc-devel mailing list > hwloc-de...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/hwloc-devel -- Jeff Squyres jsquy...@cisco.com For corporate legal information go to: http://www.cisco.com/web/about/doing_business/legal/cri/
