Re: [PATCH 1/2] lib: more scalable list_sort()

From: Artem Bityutskiy
Date: Thu Jan 21 2010 - 04:24:58 EST

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

static int list_check(void *priv, struct list_head *head,
int (*cmp)(void *priv, struct list_head *a,
struct list_head *b))
/* Checking */
#define list_check(priv, head, cmp) 0

This will provide more confidence in the algorithm correctness for
everyone who modifies 'list_sort()'.

Best Regards,
Artem Bityutskiy (ÐÑÑÑÐ ÐÐÑÑÑÐÐÐ)

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