Messages in this thread | | | Date | Fri, 20 Aug 2010 08:58:22 -0500 | From | Robin Holt <> | Subject | Re: [Patch] numa:x86_64: Cacheline aliasing makes for_each_populated_zone extremely expensive -V2. |
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On Thu, Aug 19, 2010 at 03:54:36PM -0700, H. Peter Anvin wrote: > On 08/18/2010 11:30 AM, Robin Holt wrote: > > > > - node_data[nodeid] = early_node_mem(nodeid, start, end, pgdat_size, > > + /* > > + * Allocate an extra cacheline per node to reduce cacheline > > + * aliasing when scanning all node's node_data. > > + */ > > + cache_alias_offset = nodeid * SMP_CACHE_BYTES; > > + node_data[nodeid] = cache_alias_offset + > > + early_node_mem(nodeid, start, end, > > + pgdat_size + cache_alias_offset, > > SMP_CACHE_BYTES); > > - if (node_data[nodeid] == NULL) > > + if (node_data[nodeid] == (void *)cache_alias_offset) > > return; > > nodedata_phys = __pa(node_data[nodeid]); > > reserve_early(nodedata_phys, nodedata_phys + pgdat_size, "NODE_DATA"); > > I'm concerned about this, because it really seems to rely on subtleties > in the behavior of early_node_mem, as well as the direction of > find_e820_area -- which is pretty much intended to change anyway. It's > the "action at a distance" effect. > > What we really want, I think, is to push the offsetting into > find_early_area(). Right now we have an alignment parameter, but what > we need is an alignment and a color parameter (this is just a classic > case of cache coloring, after all) which indicates the desirable offset > from the alignment base.
That sounds reasonable. Are there other examples you can think of which I can build upon?
Robin
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