[Xen-devel] [PATCH 1 of 3] xentrace: correct formula to calculate t_info_pages

[Olaf Hering <olaf@xxxxxxxxx>]

# HG changeset patch
# User Olaf Hering <olaf@xxxxxxxxx>
# Date 1301423840 -7200
# Node ID 8a2ce5e49b2c5f2e013734b5d53eae37572f4101
# Parent  45eeeb6d0481efaab2a59941e1b8e061aead37d4
xentrace: correct formula to calculate t_info_pages

The current formula to calculate t_info_pages, based on the initial
code, is slightly incorrect. It may allocate more than needed.
Each cpu has some pages/mfns stored as uint32_t.
That list is stored with an offset at tinfo.

Signed-off-by: Olaf Hering <olaf@xxxxxxxxx>

---
 xen/common/trace.c |    7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff -r 45eeeb6d0481 -r 8a2ce5e49b2c xen/common/trace.c
--- a/xen/common/trace.c        Tue Mar 29 16:34:01 2011 +0100
+++ b/xen/common/trace.c        Tue Mar 29 20:37:20 2011 +0200
@@ -110,7 +110,7 @@
 {
     struct t_buf dummy;
     typeof(dummy.prod) size;
-    unsigned int t_info_words, t_info_bytes;
+    unsigned int t_info_words;
 
     /* force maximum value for an unsigned type */
     size = -1;
@@ -125,9 +125,8 @@
         pages = size;
     }
 
-    t_info_words = num_online_cpus() * pages + t_info_first_offset;
-    t_info_bytes = t_info_words * sizeof(uint32_t);
-    t_info_pages = PFN_UP(t_info_bytes);
+    t_info_words = num_online_cpus() * pages * sizeof(uint32_t);
+    t_info_pages = PFN_UP(t_info_first_offset + t_info_words);
     printk(XENLOG_INFO "xentrace: requesting %u t_info pages "
            "for %u trace pages on %u cpus\n",
            t_info_pages, pages, num_online_cpus());

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