[Xen-changelog] [xen-unstable] x86/HPET: don't needlessly set up channels for broadcast

[Xen patchbot-unstable <patchbot@xxxxxxx>]

# HG changeset patch
# User Jan Beulich <jbeulich@xxxxxxxx>
# Date 1348817142 -7200
# Node ID b7de1713ab8d280b36ebad86254801bea5041537
# Parent  41f523f1b5e5af9cf8e85160f2412456da83050f
x86/HPET: don't needlessly set up channels for broadcast

When there are more FSB delivery capable HPET channels than CPU cores
(or threads), we can simply use a dedicated channel per CPU. This
avoids wasting the resources to handle the excess channels (including
the pointless triggering of the respective interrupt on each
wraparound) as well as the ping-pong of the interrupts' affinities
(when getting assigned to different CPUs).

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Acked-by: Keir Fraser <keir@xxxxxxx>
---


diff -r 41f523f1b5e5 -r b7de1713ab8d xen/arch/x86/hpet.c
--- a/xen/arch/x86/hpet.c       Fri Sep 28 09:23:34 2012 +0200
+++ b/xen/arch/x86/hpet.c       Fri Sep 28 09:25:42 2012 +0200
@@ -369,7 +369,7 @@ static void __init hpet_fsb_cap_lookup(v
     if ( !hpet_events )
         return;
 
-    for ( i = 0; i < num_chs; i++ )
+    for ( i = 0; i < num_chs && num_hpets_used < nr_cpu_ids; i++ )
     {
         struct hpet_event_channel *ch = &hpet_events[num_hpets_used];
         u32 cfg = hpet_read32(HPET_Tn_CFG(i));
@@ -408,6 +408,9 @@ static struct hpet_event_channel *hpet_g
     if ( num_hpets_used == 0 )
         return hpet_events;
 
+    if ( num_hpets_used >= nr_cpu_ids )
+        return &hpet_events[cpu];
+
     do {
         next = next_channel;
         if ( (i = next + 1) == num_hpets_used )

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