From owner-cvs-src  Sat Feb 15 17:24:40 2003
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Date: Sun, 16 Feb 2003 12:25:10 +1100 (EST)
From: Bruce Evans <bde@zeta.org.au>
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To: Juli Mallett <jmallett@FreeBSD.org>
Cc: Kirk McKusick <mckusick@FreeBSD.org>,
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Subject: Re: cvs commit: src/sbin/newfs mkfs.c src/sys/ufs/ffs ffs_alloc.c
 ffs_vfsops.c
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On Fri, 14 Feb 2003, Juli Mallett wrote:

> * De: Kirk McKusick <mckusick@FreeBSD.org> [ Data: 2003-02-14 ]
> 	[ Subjecte: cvs commit: src/sbin/newfs mkfs.c src/sys/ufs/ffs ffs_alloc.c ffs_vfsops.c ]
> > mckusick    2003/02/14 13:31:58 PST
> >
> >   Modified files:
> >     sbin/newfs           mkfs.c
> >     sys/ufs/ffs          ffs_alloc.c ffs_vfsops.c
> >   Log:
> >   Replace use of random() with arc4random() to provide less guessable
> >   values for the initial inode generation numbers in newfs and for
> >   newly allocated inode generation numbers in the kernel.
>
> Are the sequences for it also repeatable in the newfs case for e.g. the
> regression tests, where it is used unseeded?

Probably not.

Randomness caused me problems in the kernel when I tried to figure out
why soft-updates allocated blocks more 10-30% more pessimally than
!soft-updates (for the benchmark of reading back files in creation
order after untarring /usr/src to a new file system and remounting).
I just ifdefed out the randomness, but should have done more for
cylinder group allocation since the pessimization might depend on
that.  IIRC, soft-updates gives some randomness anyway because it
delays some allocations.  The pessimization seemed to have something
to do with not putting blocks in such a good place for delayed
allocations.

Bruce


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