Re: [boost] serialization performance

From: Robert Ramey (ramey_at_[hidden])
Date: 2005-11-12 21:00:51

Martin Slater wrote:
>  > I believe the intel machine has hardware instructions which
> implement
>> strcmp and that compilers support them.  So even if strcmp is the
>> bottleneck, I wouldn't expect it to show up on the profiler unless
>> some sort of inlining were turned off.  Or maybe the vtune profiler
>> has special provision for these cases somewhere.
>
> VTune doesn't have any special provision for this, if a function is
> inlined it will just show up in the function it inlined it to. Under
> VC
> by default strcmp is just a regular function call but you can enable
> it
> as a compiler intrinsic (#pragma intrinsic(strcmp) ) and the compiler
> may well then generate much better code (I know enabling memcpy this
> way can reduce memcpy(&a, &b, sizeof(int)) to a simple register mov
> in places).
>
>>
>> I did check to verify that the strcmp in the type-id lookup has been
>> removed.  Instead we just make sure there is only one instance
>> of a particular extended_type_info record so that we can
>> just compare the addresses.  There are still some optimizations
>
> This is very good, I was looking at how to do this myself so am very
> happy I now don't have to;)
>
>> to be implemented - but I can't predict how much they will
>> speed up anything.
>
> Predication in optimisation I have found to be nigh on impossible,
> without a profiler or at the very least extemely heavy instrumentation
> within you code you will always get a shock as to where the time is
> spent. VC6 was a nightmare in this regard as for example it would not
> inline some trivial functions without being given __forceinline for
> that function casuing some potentially extrememly fast code to run
> pathetically slowly.
>
> If your interested in vtune they do an evaluation verion at
> https://registrationcenter.intel.com/EvalCenter/EvalForm.aspx?ProductID=319
> It is simply the best profiling tool I have ever used.
>
> I'd be more than happy to help out with any profiling and
> optimisation I can.
>
>
> Martin.