Re: [PATCH 2/3] x86/hash: swap parameters of crc32_u32()

[Daniel Borkmann]

On 02/24/2014 11:53 AM, Jan Beulich wrote:
> > > > On 24.02.14 at 11:22, Daniel Borkmann <dborkman@xxxxxxxxxx> wrote:
> > On 02/24/2014 09:03 AM, Jan Beulich wrote:
> > > > > > On 22.02.14 at 13:09, Daniel Borkmann <dborkman@xxxxxxxxxx> wrote:
> > > > On 02/21/2014 11:33 AM, Jan Beulich wrote:
> > > > > ... to match its two callers (i.e. the alternative would have been to
> > > > > swap the arguments at the call sites).
> > > > >
> > > > > Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> > > > > Cc: Francesco Fusco <ffusco@xxxxxxxxxx>
> > > > > Cc: Daniel Borkmann <dborkman@xxxxxxxxxx>
> > > > > Cc: Thomas Graf <tgraf@xxxxxxxxxx>
> > > > > Cc: David S. Miller <davem@xxxxxxxxxxxxx>
> > > > > ---
> > > > >     arch/x86/lib/hash.c |    2 +-
> > > > >     1 file changed, 1 insertion(+), 1 deletion(-)
> > > > >
> > > > > --- 3.14-rc3-x86-hash-crc32.orig/arch/x86/lib/hash.c
> > > > > +++ 3.14-rc3-x86-hash-crc32/arch/x86/lib/hash.c
> > > > > @@ -37,7 +37,7 @@
> > > > >     #include <asm/cpufeature.h>
> > > > >     #include <asm/hash.h>
> > > > >
> > > > > -static inline u32 crc32_u32(u32 crc, u32 val)
> > > > > +static inline u32 crc32_u32(u32 val, u32 crc)
> > > > >     {
> > > > >     #ifdef CONFIG_AS_CRC32
> > > > >     	asm ("crc32l %1,%0\n" : "+r" (crc) : "rm" (val));
> > > >
> > > > Can you elaborate?
> > > >
> > > > Sorry, I need to ask here (even if it's a stupid question ;)) if this
> > > > change is safe to do; are referring to a cleanup or fixing a concrete
> > > > bug? The code is a modified version of the DPDK hash which you can find
> > > > in [1]. Arguments of the caller are in the correct order, afaik.
> > > >
> > > >      [1] http://dpdk.org/browse/dpdk/tree/lib/librte_hash/rte_hash_crc.h
> > >
> > > Yes, that file appears to be correct:
> > >
> > > rte_hash_crc_4byte(uint32_t data, uint32_t init_val)
> > >
> > > as opposed to
> > >
> > > static inline u32 crc32_u32(u32 crc, u32 val)
> > >
> > > (quite obviously data <-> val and crc <-> init_val, supported
> > > by the second argument in each caller being named "seed").
> >
> > If you want a more descriptive name, feel free to rename these vars,
> > but check it yourself, it's not a bug as you claim; results are the
> > same:
>
> Even if the results are the same (operands being symmetric?), check
> the generated code for your version and the fixed up one: The crc32
> instruction allows one of its operands to be in memory for a reason.

I'm fine with that. But then, please reflect these details in your
commit message.

Thanks !
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