X-Git-Url: http://git.vanrenterghem.biz/git.ikiwiki.info.git/blobdiff_plain/7bfa77380ac1fda68d224343c46b310779ce9980..6cde77d5d46fd8b7e3fa711fa535c6a3de834b1c:/doc/todo/multi-thread_ikiwiki.mdwn

diff --git a/doc/todo/multi-thread_ikiwiki.mdwn b/doc/todo/multi-thread_ikiwiki.mdwn
index 3838103ff..358185a22 100644
--- a/doc/todo/multi-thread_ikiwiki.mdwn
+++ b/doc/todo/multi-thread_ikiwiki.mdwn
@@ -35,3 +35,55 @@ Disclaimer: I know nothing of the Perl approach to parallel processing.
 > > about meet the benefit of most of the threading/async work.
 > >
 > > --[[tychoish]]
+
+>>> It's at this point that doing profiling for a particular site would come
+>>> in, because it would depend on the site content and how exactly IkiWiki is
+>>> being used as to what the performance bottlenecks would be.  For the
+>>> original poster, it would be image processing.  For me, it tends to be
+>>> PageSpecs, because I have a lot of maps and reports.
+
+>>> But I sincerely don't think that Disk I/O is the main bottleneck, not when
+>>> the original poster mentions CPU usage, and also in my experience, I see
+>>> IkiWiki chewing up 100% CPU usage one CPU, while the others remain idle.  I
+>>> haven't noticed slowdowns due to waiting for disk I/O, whether that be a
+>>> system with HD or SSD storage.
+
+>>> I agree that large sites are probably not the most common use-case, but it
+>>> can be a chicken-and-egg situation with large sites and complete rebuilds,
+>>> since it can often be the case with a large site that rebuilding based on
+>>> dependencies takes *longer* than rebuilding the site from scratch, simply
+>>> because there are so many pages that are interdependent.  It's not always
+>>> the number of pages itself, but how the site is being used.  If IkiWiki is
+>>> used with the absolute minimum number of page-dependencies - that is, no
+>>> maps, no sitemaps, no trails, no tags, no backlinks, no albums - then one
+>>> can have a very large number of pages without having performance problems.
+>>> But when you have a change in PageA affecting PageB which affects PageC,
+>>> PageD, PageE and PageF, then performance can drop off horribly.  And it's a
+>>> trade-off, because having features that interlink pages automatically is
+>>> really nifty ad useful - but they have a price.
+
+>>> I'm not really sure what the best solution is.  Me, I profile my IkiWiki builds and try to tweak performance for them... but there's only so much I can do.
+>>> --[[KathrynAndersen]]
+
+>>>> IMHO, the best way to get a multithreaded ikiwiki is to rewrite it
+>>>> in haskell, using as much pure code as possible. Many avenues
+>>>> then would open up to taking advantage of haskell's ability to
+>>>> parallize pure code.
+>>>>
+>>>> With that said, we already have some nice invariants that could be
+>>>> used to parallelize page builds. In particular, we know that
+>>>> page A never needs state built up while building page B, for any
+>>>> pages A and B that don't have a dependency relationship -- and ikiwiki
+>>>> tracks such dependency relationships, although not currently in a form
+>>>> that makes it very easy (or fast..) to pick out such groups of
+>>>> unrelated pages.
+>>>> 
+>>>> OTOH, there are problems.. building page A can result in changes to
+>>>> ikiwiki's state; building page B can result in other changes. All
+>>>> such changes would have to be made thread-safely. And would the
+>>>> resulting lock contention result in a program that ran any faster
+>>>> once parallelized?
+>>>> 
+>>>> Which is why [[rewrite_ikiwiki_in_haskell]], while pretty insane, is
+>>>> something I keep thinking about. If only I had a spare year..
+>>>> --[[Joey]]