Messages in this thread | | | Date | Thu, 21 Jan 2010 20:54:34 +1100 | From | Dave Chinner <> | Subject | Re: [PATCH 1/2] lib: more scalable list_sort() |
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On Thu, Jan 21, 2010 at 11:22:55AM +0200, Artem Bityutskiy wrote: > On Wed, 2010-01-20 at 20:51 -0800, Don Mullis wrote: > > The use of list_sort() by UBIFS looks like it could generate long > > lists; this alternative implementation scales better, reaching ~3x > > performance gain as list length approaches the L2 cache size. > > > > Stand-alone program timings were run on a Core 2 duo L1=32KB L2=4MB, > > gcc-4.4, with flags extracted from an Ubuntu kernel build. Object > > size is 552 bytes versus 405 for Mark J. Roberts' code. > > > > Worst case for either implementation is a list length just over a POT, > > and to roughly the same degree, so here are results for a range of > > 2^N+1 lengths. List elements were 16 bytes each including malloc > > overhead; random initial order. > > > > Could you please add a debugging function which would be compiled-out > normally, and which would check that on the output 'list_sort()' gives > really sorted list, and number of elements in the list stays the same. > You'd call this function before returning from list_sort(). Something > like: > > #ifdef DEBUG_LIST_SORT > static int list_check(void *priv, struct list_head *head, > int (*cmp)(void *priv, struct list_head *a, > struct list_head *b)) > { > /* Checking */ > } > #else > #define list_check(priv, head, cmp) 0 > #endif > > This will provide more confidence in the algorithm correctness for > everyone who modifies 'list_sort()'.
I'd suggest the same method as employed in lib/sort.c - a simple userspace program that verifies correct operation is included in lib/sort.c....
Cheers,
Dave. -- Dave Chinner david@fromorbit.com
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