Fwd: kqueue benchmark

Ian Lynagh ian at well-typed.com
Mon Jan 7 22:33:17 CET 2013

Thanks Andi!

Johan, could you review and (all being well) apply please?


On Sat, Jan 05, 2013 at 02:16:20PM -0500, Andreas Voellmy wrote:
> Hi Ian and Simon,
> As you may know, I've been working on an update to GHC's IO manager
> component that substantially improves the performance and scalability (with
> cores) of this component. For example, the attached graph shows the
> performance of a highly simplified web server written in Haskell vs GHC 7.7
> HEAD and vs a C web server that was written to do essentially the same
> thing as my Haskell web server, minus all the Haskell overhead. With my IO
> manager update, we get about 2x the performance of GHC 7.7 HEAD with 1
> core, and over 20x the performance when use lots of cores. We also come
> very close to the performance of the C web server. (I can give you much
> more detail on the experiment if you like - just let me know).
> Actually, this Haskell web server with the IO manager update allowed me to
> push linux hard enough to find an elusive bug in the linux kernel that has
> existed since Linux 2.6!  After finding some weird behavior with my Haskell
> web server, I wrote the C web server (the one I mentioned above) to
> simulate the Haskell code's use of the kernel, but only using C.  After a
> few weeks of work, the kernel developers found a missing memory barrier and
> committed a patch to Linux:
> https://github.com/torvalds/linux/commit/128dd1759d96ad36c379240f8b9463e8acfd37a1
> .
> Bryan O'Sullivan recently reviewed my commits and has suggested that I now
> ask you to pull changes into GHC. My changes required two minor commits to
> the main repository and lots of commits to the base library repository.
> I've posted my work on github:
> main repository:
> https://github.com/AndreasVoellmy/ghc-arv/tree/parallel-iomanager-reimp-2
> (last two commits)
> and base library repository:
> https://github.com/AndreasVoellmy/ghc-base-arv/tree/parallel-iomanager-reimp-5
> (all commits following 3fb1aac)
> You may not want to review all the commits in my base library repo, but it
> would be great if you could look at the two commits in the main repo,
> because they add a couple hooks from the RTS to the IO manager.
> Let me know if you need any more clarification or more revisions. I'm not
> sure exactly what the correct protocol is for getting these changes in, so
> let me know if I need to do something like open a ticket, etc.
> Cheers,
> Andi
> ---------- Forwarded message ----------
> From: Bryan O'Sullivan <bos at serpentine.com>
> Date: Fri, Jan 4, 2013 at 11:43 AM
> Subject: Re: kqueue benchmark
> To: Andreas Voellmy <andreas.voellmy at gmail.com>
> Cc: Johan Tibell <johan.tibell at gmail.com>, Kazu Yamamoto <kazu at iij.ad.jp>
> Thanks, Andi. At this point, I think you should just go ahead and ask Ian
> or Simon to pull your work into the relevant ghc trees. It's looking great.
> On Jan 4, 2013, at 8:39, Andreas Voellmy <andreas.voellmy at gmail.com> wrote:
> Bryan: thanks for the detailed review and comments! I've gone through all
> of your comments and for almost all of them I made the change you suggested
> (I.e.  fixing the mistake in calling eventfd_write, improving comments,
> reducing use of conditional compiles, etc.). The only exceptions were (1)
> one minor tidying up change you suggested that became obsolete due to a
> later change and (2) the comment on reducing the number of capabilities at
> runtime. For this one, you asked whether the RTS supports it. It does
> support it. You also mentioned that it seems a bit complex. I agree, but I
> don't think it's too bad, so I've just left it alone.
> I also made a couple commits to address things with closeFdWith, closeFd,
> and closeFd_ that I mentioned in my last email.
> I pushed a new branch here:
> https://github.com/AndreasVoellmy/ghc-base-arv/tree/parallel-iomanager-reimp-5
> It has been rebased against the latest HEAD and includes the following new
> commits:
> These address Bryan's comments:
> f33364a Fix wrong type in FFI call to eventfd_write in GHC.Event.Control.
> cd7e381 Avoid conditional compilation in GHC.Event.Manager.
> 7af055c Undo recent change to the type of
> GHC.Event.Thread.getSystemEventManager and update the commentary on this
> function
> These are fixes to closeFdWith, closeFd, and closeFd_:
> c925187 closeFdWith invokes callbacks only after the fd is closed.
> bb015fe Tidy up GHC.Event.Thread.closeFdWith.
> 879b0f1 closeFdWith closes fd after unregistering the fd with the backend.
> b508e1a Update closeFd_ to avoid unnecessary backend modifications.
> 44ed970 Change GHC.Event.Manager.closeFd to unregister interest in the file
> with the backend.
> 3622106 Avoid use of backend modifyFdOnce in Poll backend in unregisterFd_.
> de608e5 Added missing wakeup in GHC.Event.Manager.closeFd_.
> 639ee76 Improve comment on GHC.Event.Manager.closeFd_.
> On Mon, Dec 31, 2012 at 6:18 PM, Bryan O'Sullivan <bos at serpentine.com>wrote:
> > Last code review of 2012 finished :-)
> >
> > I've commented on all your commits on github. It's a very well put
> > together patchset, and was easy to review. Thanks for going to the extra
> > effort to make the patches small enough to be reviewable.
> >
> > There was only one obviously wrong commit, which I flagged. Apart from
> > that, the only substantial comment I had was about the increased number of
> > #ifdefs. I believe that many of those could be done away with, which would
> > make the code both cleaner and more statically checkable on more platforms
> > - I'll see if I can find time to confirm that theory.
> >
> > I'm sure you've seen that people are justifiedly rather excited about your
> > work: https://twitter.com/bos31337/status/284701554458640384
> >
> > Great work!
> > B.
> >
> > On Fri, Dec 28, 2012 at 3:26 AM, Andreas Voellmy <
> > andreas.voellmy at gmail.com> wrote:
> >
> >> The changes were almost entirely in the base package. You can find them
> >> here:
> >>
> >>
> >> https://github.com/AndreasVoellmy/ghc-base-arv/tree/parallel-iomanager-reimp-3
> >>
> >> I also had to add a couple of RTS hooks, so there are also two commits in
> >> the main repo, which you can see here:
> >>
> >> https://github.com/AndreasVoellmy/ghc-arv/tree/parallel-iomanager-reimp-2
> >>
> >
> >

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