[zeromq-dev] ØMQ VSM data alignment
matt_weinstein at yahoo.com
Wed Aug 4 19:44:59 CEST 2010
On Aug 4, 2010, at 1:37 PM, Andrew Hume wrote:
> this sort of thing can get problematic quickly.
> the combinatorial explosion of cache-line design, memory design,
> language alignment rules, architectures allowing non-aligned
> (but punishing you with slowness) makes testing hard.
> on the other hand, starting on a 8 byte boundary is always a good
> idea in modern architectures.
> better style is to use a byte stream so you won't get bitten by LSB/
> MSB issues
> or packets coming from other machine architectures.
Yes, but I want to do this:
my_struct const* pstruct = reinterpret_cast<my_struct
cout << "Works like magic: " << pstruct->member << ". All your
processor are belong to Intel! (*)" << endl;
That's the no-copy approach :-)
I can do it with malloc() without issue or penalty...
(*) There are no other architectures :-)
> On Aug 4, 2010, at 1:09 PM, Pieter Hintjens wrote:
>> I don't think this has been covered. It would be sensible to have
>> vsm_data aligned but it's something that is IMO worth testing rather
>> than doing on faith.
>>> Sorry if this has been covered before.
>>> I've been using zmq to transport raw structures, and I've noticed
>>> zeromq apparently does not provide appropriate alignment for
>>> messages in
>>> VSMs, and maybe for larger messages as well if you're using the
>>> front of the
>>> content buffer (I haven't looked :-( )
>>> Here are the offsets:
>>> 0x00 void *content;
>>> 0x08 unsigned char flags;
>>> 0x09 unsigned char vsm_size;
>>> 0x0a unsigned char vsm_data [ZMQ_MAX_VSM_SIZE];
>>> Shouldn't vsm_data be padded to 0x10 on 64 bit architectures (and
>>> zeromq-dev mailing list
>>> zeromq-dev at lists.zeromq.org
>> zeromq-dev mailing list
>> zeromq-dev at lists.zeromq.org
> Andrew Hume (best -> Telework) +1 732-886-1886
> andrew at research.att.com (Work) +1 973-360-8651
> AT&T Labs - Research; member of USENIX and LOPSA
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> zeromq-dev at lists.zeromq.org
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