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

From: Artem Bityutskiy
Date: Wed Aug 04 2010 - 10:07:05 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.

This patch breaks UBIFS. I did not have time to dig deeper, but the
symptoms is that list_sort() calls the 'cmp()' function with bogus
'struct list_head *a' parameter, which did not exist in the original

I see this on 2.6.35-rc1. Did not try the release yet. But when I revert
your patch - everything works fine.

Best Regards,
Artem Bityutskiy (ÐÑÑÑÐ ÐÐÑÑÑÐÐÐ)

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