X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=doc%2Fthreads.texi;h=77afeda0e17a49a0062062b16d6c9ba328c705b5;hb=1802b7b7b8d5e3d6754da9468e22942a8c29982b;hp=314ee61ca865aef58c4cb51cc4260eea8a965001;hpb=ef630eaec47e13ce3bda0cdc876869fc4a185e8e;p=pintos-anon

diff --git a/doc/threads.texi b/doc/threads.texi
index 314ee61..77afeda 100644
--- a/doc/threads.texi
+++ b/doc/threads.texi
@@ -185,8 +185,8 @@ project 3.  For now, you can ignore it.
 
 @item flags.h
 Macros that define a few bits in the 80@var{x}86 ``flags'' register.
-Probably of no interest.  See @bibref{IA32-v1}, section 3.4.3, for more
-information.
+Probably of no interest.  See @bibref{IA32-v1}, section 3.4.3, ``EFLAGS
+Register,'' for more information.
 @end table
 
 @menu
@@ -511,7 +511,8 @@ must be active, but we must be able to choose the 4.4@acronym{BSD}
 scheduler
 with the @option{-mlfqs} kernel option.  Passing this
 option sets @code{enable_mlfqs}, declared in @file{threads/init.h}, to
-true.
+true when the options are parsed by @func{parse_options}, which happens
+midway through @func{main}.
 
 When the 4.4@acronym{BSD} scheduler is enabled, threads no longer
 directly control their own priorities.  The @var{priority} argument to
@@ -531,6 +532,12 @@ Here's a summary of our reference solution, produced by the
 @command{diffstat} program.  The final row gives total lines inserted
 and deleted; a changed line counts as both an insertion and a deletion.
 
+The reference solution represents just one possible solution.  Many
+other solutions are also possible and many of those differ greatly from
+the reference solution.  Some excellent solutions may not modify all the
+files modified by the reference solution, and some may modify files not
+modified by the reference solution.
+
 @verbatim
  devices/timer.c       |   42 +++++-
  threads/fixed-point.h |  120 ++++++++++++++++++
@@ -591,6 +598,34 @@ to cause many of the tests to fail.
 @item How do I run the tests?
 
 @xref{Testing}.
+
+@item Why do I get a test failure in @func{pass}?
+
+@anchor{The pass function fails}
+You are probably looking at a backtrace that looks something like this:
+
+@example
+0xc0108810: debug_panic (../../lib/kernel/debug.c:32)
+0xc010a99f: pass (../../tests/threads/tests.c:93)
+0xc010bdd3: test_mlfqs_load_1 (../../tests/threads/mlfqs-load-1.c:33)
+0xc010a8cf: run_test (../../tests/threads/tests.c:51)
+0xc0100452: run_task (../../threads/init.c:283)
+0xc0100536: run_actions (../../threads/init.c:333)
+0xc01000bb: main (../../threads/init.c:137)
+@end example
+
+This is just confusing output from the @command{backtrace} program.  It
+does not actually mean that @func{pass} called @func{debug_panic}.  In
+fact, @func{fail} called @func{debug_panic} (via the @func{PANIC}
+macro).  GCC knows that @func{debug_panic} does not return, because it
+is declared @code{NO_RETURN} (@pxref{Function and Parameter
+Attributes}), so it doesn't include any code in @func{pass} to take
+control when @func{debug_panic} returns.  This means that the return
+address on the stack looks like it is at the beginning of the function
+that happens to follow @func{fail} in memory, which in this case happens
+to be @func{pass}.
+
+@xref{Backtraces}, for more information.
 @end table
 
 @menu
@@ -647,8 +682,8 @@ If multiple threads have the same highest priority,
 
 Priority donation only changes the priority of the donee
 thread.  The donor thread's priority is unchanged.  
-Priority donation is not additive: if thread @var{A} (with priority 5) donates
-to thread @var{B} (with priority 3), then @var{B}'s new priority is 5, not 8.
+Priority donation is not additive: if thread @var{A} (with priority 3) donates
+to thread @var{B} (with priority 5), then @var{B}'s new priority is 3, not 8.
 
 @item Can a thread's priority change while it is on the ready queue?
 
@@ -689,4 +724,12 @@ just before the first @func{printf} in @func{main}.  Then modify
 
 It doesn't have to.  We won't test priority donation and the advanced
 scheduler at the same time.
+
+@item Can I use one queue instead of 64 queues?
+
+Yes, that's fine.  It's easiest to describe the algorithm in terms of 64
+separate queues, but that doesn't mean you have to implement it that
+way.
+
+If you use a single queue, it should probably be sorted.
 @end table