update the geom_sched entry

svn path=/www/; revision=33945

en/projects/ideas/ideas.xml

@@ -15,7 +15,7 @@ Ideas//EN"
 <ideas>
   <cvs:keywords xmlns:cvs="http://www.FreeBSD.org/XML/CVS" version="1.0">
     <cvs:keyword name="freebsd">
-      $FreeBSD: www/en/projects/ideas/ideas.xml,v 1.110 2009/03/13 20:02:23 gabor Exp $
+      $FreeBSD: www/en/projects/ideas/ideas.xml,v 1.111 2009/03/14 10:18:18 rwatson Exp $
     </cvs:keyword>
   </cvs:keywords>
 
@@ -723,28 +723,53 @@ href="http://info.iet.unipi.it/~luigi/FreeBSD/linux_bsd_kld.html">here</a>.</p>
       </idea>
 
       <idea id="psched">
-	<title>Pluggable Disk Scheduler</title>
+	<title>Geom-based Disk Schedulers</title>
 
 	<desc>
 <p><strong>Technical contact</strong>: <a
-  href="mailto:s223560@studenti.ing.unipi.it">Emiliano Mennucci</a></p>
+  href="mailto:luigi@freebsd.org">Luigi Rizzo</a></p>
 <p><strong>References</strong>: <a
   href="http://wiki.freebsd.org/moin.cgi/Hybrid">The Pluggable Disk
   Schedulers SoC project</a>, <a
   href="http://www.happyemi.org/hybrid/">Patches</a></p>
-<p>Our "Pluggable Disk Schedulers" SoC 2005 project resulted in code which
-  solved the problem where large sequential I/O requests, or certain
-  access patterns from one or a few processes, might almost completely
-  starve other processes.  It is available as a patch for RELENG_4 and
-  RELENG_5.  Unfortunately the code in FreeBSD-current (and RELENG_6)
-  changed too much, so that the patches can not be committed.  The goal
-  of this project is to port the pluggable disk schedulers to the GEOM
-  framework.</p>
-<p>Interested people should also have a look at <a
-  href="http://lists.freebsd.org/pipermail/freebsd-geom/2007-January/001854.html">
-  a mail thread about this</a> (Ulf is not working on this) and <a
-  href="http://www.freebsd.org/cgi/mid.cgi?db=irt&amp;id=20071011022001.GC13480@gandalf.sssup.it">
-  further discussion</a> of the corresponding GEOM aspects.</p>
+<p>In a 2005 GSoC project, "Pluggable Disk Schedulers", Emiliano
+  Mennucci explored the feasibility of pluggable disk schedulers
+  for FreeBSD. The project was successful, but we could not explore
+  certain approaches (e.g. "anticipation", where requests are delayed
+  hoping that some future ones can served without a seek) due to
+  architectural limitations the kernel had at the time.
+  <p>
+  Since then, the GEOM infrastructure has become available on FreeBSD
+  for interacting with disk I/O requests. GEOM has enabled us to
+  work on disk schedulers in a much more flexible way, allowing a
+  much faster development of disk scheduling algorithms. With
+  Fabio Checconi, we have developed a prototype
+  implementation of some anticipatory schedulers, see
+  <a href="http://info.iet.unipi.it/~luigi/FreeBSD/#geom_sched">GEOM_SCHED</a>.
+  <p>
+  GEOM_SCHED works within the geom layer, i.e. above the device driver
+  where queueing of requests may actually occur. The way GEOM_SCHED
+  does scheduling is by limiting the number of outstanding requests
+  to the device, and the performance implications of this approach
+  need to be measured. An alternative approach is to push the
+  scheduler (using the same algorithms developed in GEOM_SCHED,
+  and most likely the same code) within the device drivers. This less general
+  (as it needs to be replicated in all drivers) but it may be
+  an interesting thing to do e.g. for some popular device drivers
+  such as ATA.
+  <p>
+  The proposed SoC work can address one or more of the following
+  aspects:
+  i) implement suitable classifiers for
+  disk requests; ii) implement techniques for the auto-tuning of
+  the scheduler parameters; iii) measure the performance implications
+  of doing scheduling above the device driver, and possibly design
+  and implement a suitable mechanism to push the GEOM_SCHED
+  module within the device driver itself.
+  <p>
+Ultimately, we expect to end up with a production quality subsystem
+for use in FreeBSD.
+
 <p><strong>Requirements</strong>:</p>
 <ul>
   <li>Ability to read and understand foreign C code.</li>