Messages in this thread | | | Date | Wed, 29 Jan 2020 12:10:13 -0600 | From | Scott Cheloha <> | Subject | Re: [PATCH] powerpc/drmem: cache LMBs in xarray to accelerate lookup |
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On Tue, Jan 28, 2020 at 05:56:55PM -0600, Nathan Lynch wrote: > Scott Cheloha <cheloha@linux.ibm.com> writes: > > LMB lookup is currently an O(n) linear search. This scales poorly when > > there are many LMBs. > > > > If we cache each LMB by both its base address and its DRC index > > in an xarray we can cut lookups to O(log n), greatly accelerating > > drmem initialization and memory hotplug. > > > > This patch introduces two xarrays of of LMBs and fills them during > > drmem initialization. The patch also adds two interfaces for LMB > > lookup. > > Good but can you replace the array of LMBs altogether > (drmem_info->lmbs)? xarray allows iteration over the members if needed.
I don't think we can without potentially changing the current behavior.
The current behavior in dlpar_memory_{add,remove}_by_ic() is to advance linearly through the array from the LMB with the matching DRC index.
Iteration through the xarray via xa_for_each_start() will return LMBs indexed with monotonically increasing DRC indices.
Are they equivalent? Or can we have an LMB with a smaller DRC index appear at a greater offset in the array?
If the following condition is possible:
drmem_info->lmbs[i].drc_index > drmem_info->lmbs[j].drc_index
where i < j, then we have a possible behavior change because xa_for_each_start() may not return a contiguous array slice. It might "leap backwards" in the array. Or it might skip over a chunk of LMBs.
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