From bf9e4143b34fe8b24fcda3279265058a71aa50da Mon Sep 17 00:00:00 2001
From: Andreas Kloeckner <inform@tiker.net>
Date: Wed, 5 Feb 2014 16:34:17 -0600
Subject: [PATCH] Update the tutorial for fixed slab bound generation
---
doc/tutorial.rst | 37 +++++++++++++++++++++++++------------
1 file changed, 25 insertions(+), 12 deletions(-)
diff --git a/doc/tutorial.rst b/doc/tutorial.rst
index d8a982e6c..72c6c5b0c 100644
--- a/doc/tutorial.rst
+++ b/doc/tutorial.rst
@@ -625,7 +625,7 @@ loop's tag to ``"unr"``:
:func:`loopy.tag_inames` is a new transformation that assigns
-implementation tags to kernels. ``"unr'`` is the first tag we've
+implementation tags to kernels. ``"unr"`` is the first tag we've
explicitly learned about. Technically, though, it is the second--``"for"``
(or, equivalently, *None*), which is the default, instructs loopy to
implement an iname using a for loop.
@@ -747,10 +747,12 @@ assumption:
...
While these conditionals enable the generated code to deal with arbitrary
-*n*, they come at a performance cost. But there's still no reason to pay
-for them with *every* item processed. Loopy allows generating separate code
-for the last iteration of the loop, by using the *slabs* keyword argument
-to :func:`split_iname`:
+*n*, they come at a performance cost. Loopy allows generating separate code
+for the last iteration of the *i_outer* loop, by using the *slabs* keyword
+argument to :func:`split_iname`. Since this last iteration of *i_outer* is
+the only iteration for which ``i_inner + 4*i_outer`` can become larger than
+*n*, only the (now separate) code for that iteration contains conditionals,
+enabling some cost savings:
.. doctest::
@@ -759,16 +761,27 @@ to :func:`split_iname`:
>>> knl = lp.set_options(knl, "write_cl")
>>> evt, (out,) = knl(queue, a=x_vec_dev)
<BLANKLINE>
- for (int i_outer = 0; i_outer <= (-1 + ((3 + n) / 4)); ++i_outer)
+ ...
+ /* bulk slab for 'i_outer' */
+ for (int i_outer = 0; i_outer <= (-2 + ((3 + n) / 4)); ++i_outer)
{
a[0 + i_outer * 4] = 0.0f;
- if ((-2 + -4 * i_outer + n) >= 0)
- a[1 + i_outer * 4] = 0.0f;
- if ((-3 + -4 * i_outer + n) >= 0)
- a[2 + i_outer * 4] = 0.0f;
- if ((-4 + -4 * i_outer + n) >= 0)
- a[3 + i_outer * 4] = 0.0f;
+ a[1 + i_outer * 4] = 0.0f;
+ a[2 + i_outer * 4] = 0.0f;
+ a[3 + i_outer * 4] = 0.0f;
}
+ /* final slab for 'i_outer' */
+ for (int i_outer = (-1 + n + -1 * (3 * n / 4)); i_outer <= (-1 + ((3 + n) / 4)); ++i_outer)
+ if ((-1 + n) >= 0)
+ {
+ a[0 + i_outer * 4] = 0.0f;
+ if ((-2 + -4 * i_outer + n) >= 0)
+ a[1 + i_outer * 4] = 0.0f;
+ if ((-3 + -4 * i_outer + n) >= 0)
+ a[2 + i_outer * 4] = 0.0f;
+ if ((4 + 4 * i_outer + -1 * n) == 0)
+ a[3 + i_outer * 4] = 0.0f;
+ }
...
.. _specifying-arguments:
--
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