"make delete-old" performance.

b. f. bf1783 at googlemail.com
Thu May 17 03:18:47 UTC 2012

> I recently ran "make delete-old" on a -current box and felt it was
> rather slow.  That prompted me to do some more careful experiments.
> On one box where I have both 8-stable and 9-stable available, there
> was a ~30x slowdown (based on 5 runs, ignoring the first).  I don't
> have a -current world on that box so I can't directly compare but on
> another pair of fairly similar boxes, I get a ~180x slowdown between
> 8-stable and -current (and that figure is probably optimistic since
> the -current box was idle whereas the 8-stable box was fairly busy).
> I realise that "make delete-old" isn't something you nede to do every
> day but going from sub-second to multi-minute duration is quite
> noticable.  Can anyone suggest what has caused the change?

The slowdown is probably due - at least in part - to two factors:

- the list of files to be checked for removal has grown substantially,
because missing entries for old knobs and new entries for new knobs
have been added; and

- a new (and slower) method of checking was added in:
because the old method broke down with the size of the new lists of files.

Some changes could be made to lessen the affect of the latter.


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