[botan-devel] Threaded Filters/Operation Parallelisation

Joel Low joel at joelsplace.sg
Mon Jan 7 09:18:13 EST 2013


Hi Jack,

Yes, it's to cache the size of m_threads. That's my practice when I know
that the value is invariant, I think it's to help the compiler see that
m_threads doesn't change its size throughout the execution of the loop,
which hopefully allows it to produce better code. I think the inlining bit
is secondary since IIRC the C++ standard does dictate the behaviour of the
STL types.

I've not tested it, and it could just be me being overly cautious (or
pessimistic about my compiler). If your version fits the rest of the library
better, then I think we should go with your style.

Regards,
Joel

-----Original Message-----
From: botan-devel [mailto:botan-devel-bounces at randombit.net] On Behalf Of
Jack Lloyd
Sent: Monday, 7 January 2013 8:10 PM
To: Botan development list
Subject: Re: [botan-devel] Threaded Filters/Operation Parallelisation

Hi Joel,

I'm curious about this loop in basefilt.cpp

   for(size_t i = 0, j = m_threads.size(); i != j; ++i)
      {
      m_threads[i]->join();
      }

Is the intent here for j to simply cache m_threads.size()? Why not simply

   for(size_t i = 0; i != m_threads.size(); ++i)

as vector.size should be inlined and very fast.

-Jack


On Wed, Jan 02, 2013 at 11:01:12PM +0000, Joel Low wrote:
> Thanks for the review, Jack.
> 
> I've included the updated patch. Let me know if that works.
> 
> Regards,
> Joel
> 
> -----Original Message-----
> From: botan-devel [mailto:botan-devel-bounces at randombit.net] On Behalf 
> Of Jack Lloyd
> Sent: Wednesday, 2 January 2013 11:49 PM
> To: Botan development list
> Subject: Re: [botan-devel] Threaded Filters/Operation Parallelisation
> 
> Hi Joel,
> 
> I've only had time to very briefly review the patch but it looks good.
> 
> A few minor comments:
> 
> - Can you use an m_ prefix on all class members? I know a lot of the
>   code doesn't use a prefix or suffix at all, but I am trying to
>   ensure that all new or heavily touched code adopts m_ (rather than
>   suffix _ as you use in Semaphore or no prefix).
> 
> - Semaphore seems generally useful, move it to 
> src/util/semaphore.{cpp,h}
> 
> - Add your name to the copyright headers of each modified file. (And
>   make sure all new sources have one)
> 
> - For some reason, despite all your work on Windows support and other
>   patches, your name is not already included in the list of copyright
>   owners in the license, so please also update license.rst
> 
> Can you make those changes and send the updated patch as an attachment 
> to the list (so it can be archived by mailman)?
> 
> Thanks,
>   Jack
> 
> On Wed, Jan 02, 2013 at 06:51:10AM +0000, Joel Low wrote:
> > Hello all,
> > 
> > So I've finally managed to sit down and write this patch. The design 
> > seems quite different from what I had in mind, since this round I 
> > wanted it to be a drop-in replacement for Fork.
> > 
> > There's a bit of code taken from a blog post to emulate a semaphore: 
> > The link is there, and if someone knows of a better class (or better 
> > still, one within Botan itself), let me know and I'll use that class
> instead.
> > 
> > Let me know what you think.
> > 
> > Patch: http://pastebin.com/kgF0b7Yp (1 month visibility)
> > 
> > Regards,
> > Joel
> > 
> > -----Original Message-----
> > From: botan-devel-bounces at randombit.net 
> > [mailto:botan-devel-bounces at randombit.net] On Behalf Of Joel Low
> > Sent: Tuesday, 24 April 2012 5:07 PM
> > To: botan-devel at randombit.net
> > Subject: [botan-devel] Threaded Filters/Operation Parallelisation
> > 
> > Hello all,
> > 
> > Recently I've been playing with the idea of having a threaded Fork 
> > filter to be used together with Pipe: processing for each subsequent 
> > filter downstream of the threaded Fork filter is done in a separate 
> > thread of its own. This could potentially bring performance benefits 
> > (in theory) especially with a move on to having an increasing number 
> > of
> computing cores per CPU.
> > 
> > So I've emailed Jack separate to the list to get some of his opinions. 
> > The main points he raised were that:
> > 
> >  - The approach used for Fork would be most promising in terms of 
> > working with the current design and not forcing a full rewrite of 
> > the
> filter system.
> >  - He proposed defining a new Filter subclass Threaded_Filter which 
> > itself takes a Filter* as an argument which will spawn a thread and 
> > uses two message queues for I/O with the filter it manages.
> >  - When write() is called on the Threaded_Filter, it pushes it to 
> > the input queue, which the worker thread pulls off and write()s to 
> > the underlying filter.
> >  - With this approach the application can control concurrency very 
> > finely (perhaps too finely), since the application can specify which 
> > filters run on the main thread, and what runs on a secondary thread.
> > 
> > I was leaning to a slightly different approach: with the knowledge 
> > that Fork operations parallelise the easiest, I should adapt the 
> > Fork class to let each downstream filter run in a separate thread. 
> > This shares much commonality in its design with Jack's idea 
> > (especially in terms of thread sync and friends), provides a little 
> > less control over what runs in a separate thread, but comes with a 
> > slightly easier
> implementation.
> > 
> > Jack stated that I probably should email the devel list and solicit 
> > ideas, since everyone may have different expectations. I'll be 
> > implementing this in my spare time so I'd like to accept as many 
> > ideas and combine them before acting on it. I think that the 
> > pipe/filter design Botan has is intuitive, and I'd like to keep that 
> > as much as possible, without compromising on potential performance
gains.
> > Intuitively, both seem to run contrary to each other, but I think we 
> > can work something out here to an API that is both powerful yet 
> > easily
> mastered.
> > 
> > Any thoughts?
> > 
> > Regards,
> > Joel
> > 
> 
> 
> 
> > _______________________________________________
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> > botan-devel at randombit.net
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> 
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