Re: [PATCH] Add core.trustlowlevelstat for diffs in dev,ino,uid and gid

[Kjetil Barvik <barvik@broadpark.no>]

Linus Torvalds <torvalds@linux-foundation.org> writes:

> On Sun, 26 Apr 2009, Junio C Hamano wrote:
>> I like the end result.
>> 
>> But I am not sure about dropping the nanosecond resolution timestamps.
>> The area was extended recently in preparation for ext4; we can take
>> advantage of it to reduce the chance the racy-git avoidance codepath
>> triggers if we keep it.
>> 
>>     fba2f38 (make USE_NSEC work as expected, 2009-02-19)
>> 
>>     c06ff49 (Record ns-timestamps if possible, but do not use it without
>>     USE_NSEC, 2009-03-04)
>
> Hey, we can leave the NSEC support in. Admittedly removing that was about 
> half the patch, but even with it left in, it would be a cleanup.

  I think we should have the NSEC support, as it is a performance
  impromvent, at least on my laptop.  OK, not a huge improvment, but
  still.

  For git version 1.6.3.rc3 I made a litle test, and the difference was
  the following for the 'git checkout my-v2.6.25' (from my-v2.6.27):

                 for git compiled with    for git compiled without
                 'make USE_NSEC=1 ...':   the 'USE_NSEC=1' part:

   OK open calls:       13872                   14386
   OK close calls:      13872                   14386
   OK mmap2 calls:        102                     649
   OK munmap calls:        61                     608

  so, an improvment of 514 open() and close() calls, and 547 mmap2() and
  munmap() calls, for this particular test on my particular slow laptop
  disk.

  As I wrote in fba2f38 I would guess that the improvment is larger for
  a faster disk, and a SSD disk should be able to see a larger
  improvment that I did above.

  -- kjetil