No strong opinion. However, the comment about the initial value of opal_cache_line_size is wrong (opal/runtime/opal.h), as it states that the default value is -1 while it is 128.
george. On Apr 23, 2012, at 16:21 , Jeffrey Squyres wrote: > No one replied to this RFC. Does anyone have an opinion about it? > > I have attached a patch (including some debugging output) showing my initial > implementation. If no one objects by the end of this week, I'll commit to > the trunk. > > Terry: please add this to the agenda tomorrow. > > > On Mar 30, 2012, at 1:09 PM, Jeffrey Squyres wrote: > >> I was just recently reminded of a comment that is near the top of >> opal_init_util(): >> >> /* JMS See note in runtime/opal.h -- this is temporary; to be >> replaced with real hwloc information soon (in trunk/v1.5 and >> beyond, only). This *used* to be a #define, so it's important >> to define it very early. */ >> opal_cache_line_size = 128; >> >> A few points: >> >> 1. On my platforms, hwloc tells me that my cache line size is 64, not 128. >> Probably not a tragedy, but... >> >> 2. I see opal_cache_line_size being used in a lot of BTL and PML >> initialization locations. I see it being used in opal/class/free_list.*, >> too. >> >> 3. I poked around with this yesterday to see if we could have hwloc >> initialize the opal_cache_line_size value. Points to remember: >> >> - we initialize the opal hwloc framework in opal_init(), but we do not load >> the local machine's architecture then (because it can be expensive, >> particularly if lots of MPI processes are all doing it simultaneously) >> - instead, the local machine topology is discovered once by each orted >> (using hwloc) and then RML sent to each local MPI process, where it is >> locally loaded into each MPI proc's hwloc tree >> - this happens during the orte_init() in ompi_mpi_init() >> >> Meaning: we can initialize the opal_cache_line_size in MPI processes during >> orte_init(). >> >> Is this acceptable to everyone? >> >> If so, I can go ahead and code this up. I would probably leave the initial >> value hard-coded to 128 (just in case something uses it before orte_init()), >> and then later during orte_init(), reset it to the smallest L1 cache size >> that hwloc finds on the machine. >> >> -- >> Jeff Squyres >> jsquy...@cisco.com >> For corporate legal information go to: >> http://www.cisco.com/web/about/doing_business/legal/cri/ >> >> >> _______________________________________________ >> devel mailing list >> de...@open-mpi.org >> http://www.open-mpi.org/mailman/listinfo.cgi/devel > > > -- > Jeff Squyres > jsquy...@cisco.com > For corporate legal information go to: > http://www.cisco.com/web/about/doing_business/legal/cri/ > <opal-cache-line-size.diff>_______________________________________________ > devel mailing list > de...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/devel
