Date: Tue, 23 Sep 2008 08:37:27 -0700 From: Sam Leffler <sam@freebsd.org> To: obrien@freebsd.org Cc: cvs-src@freebsd.org, src-committers@freebsd.org, cvs-all@freebsd.org Subject: Re: cvs commit: src/sys/conf files src/sys/fs/tmpfs tmpfs.h tmpfs_subr.c tmpfs_vnops.c src/sys/i386/i386 bios.c src/sys/ia64/ia64 efi.c sal.c src/sys/libkern memcmp.c src/sys/mips/mips support.S src/sys/sys libkern.h Message-ID: <48D90D37.4000808@freebsd.org> In-Reply-To: <20080923151353.GC50098@dragon.NUXI.org> References: <200809231446.m8NEkQev007507@repoman.freebsd.org> <48D9038B.3040000@freebsd.org> <20080923151353.GC50098@dragon.NUXI.org>
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David O'Brien wrote:
> On Tue, Sep 23, 2008 at 07:56:11AM -0700, Sam Leffler wrote:
>
>> David E. O'Brien wrote:
>>
>>> obrien 2008-09-23 14:45:10 UTC
>>> FreeBSD src repository
>>> Modified files:
>>> sys/conf files sys/fs/tmpfs tmpfs.h
>>> tmpfs_subr.c tmpfs_vnops.c sys/i386/i386 bios.c
>>> sys/ia64/ia64 efi.c sal.c sys/mips/mips support.S
>>> sys/sys libkern.h Added files:
>>> sys/libkern memcmp.c Log:
>>> SVN rev 183299 on 2008-09-23 14:45:10Z by obrien
>>> The kernel implemented 'memcmp' is an alias for 'bcmp'. However,
>>> memcmp
>>> and bcmp are not the same thing. 'man bcmp' states that the return is
>>> "non-zero" if the two byte strings are not identical. Where as,
>>> 'man memcmp' states that the return is the "difference between the
>>> first two differing bytes (treated as unsigned char values" if the
>>> two byte strings are not identical.
>>> So provide a proper memcmp(9), but it is a C implementation not a
>>> tuned
>>> assembly implementation. Therefore bcmp(9) should be preferred over
>>> memcmp(9).
>>>
>>>
>> Given the performance difference this change should have been reviewed
>> before dumping it into the tree.
>>
>
>
>> I do not agree with this;
>>
>
> You do not agree with fixing a bug in our code?
>
You don't have to "fix a bug in our code" in this way. You could have,
for example, fixed the cases where the return result was checked against
!{0,1}. Then after having an implementation that was comparable in
performance to bcmp switched over completely.
>
>> did you post it somewhere?
>>
>
> No.
>
>
I suggest you need to get changes of this sort reviewed and/or you need
to show you haven't introduced a performance regression.
Sam
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