On Fri, 20 Jun 2008, David Berry wrote:
> 2008/6/20 Tim Jenness <[log in to unmask]>:
>> On Fri, 20 Jun 2008, Peter W. Draper wrote:
>>> On Fri, 20 Jun 2008, Tim Jenness wrote:
>>>> 27322 (dberry):
>>>> hds: Speed up the packing and unpacking of Structure Record
>>> Begs the question, by how much?
>> From an email David wrote to me:
>> "But even having made this change, vtune was still saying that 25% of
>> the time is spent in hds_unpack_srv, so I had a look at the
>> hds_unpack_srv.c file (and the corresponding hds_pack_srv.c file).
>> These files convert between little endian integers stored in the disk
>> file and native endian integers needed by the processor. I've
>> re-worked the algorithm written by Brian to do this, and got a further
>> decrease in run time from 118 seconds to 87 seconds. I have committed
>> these changes."
>> so pretty impressive. I'm a bit confused as to why it needed to convert at
>> all though because I thought the files were made on an intel linux box so
>> reading on an intel linux box should not require endian conversion.
Hmm not sure about this interpretation, looking at that I'd say that the
disk-order of the bytes is fixed (as it must for the record-oriented
meta-data, I'd only expect the data itself to be native), and all that
this code does is pack and unpack that as written (so there's no actual
swapping, that's just the unpack doing the reverse of the pack).