[ 3.5.y.z extended stable ] Patch "xen/time: remove blocked time accounting from xen "clockchip"" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    xen/time: remove blocked time accounting from xen "clockchip"

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 777f3829475b1b5a4955cf9563dd821b382388ff Mon Sep 17 00:00:00 2001
From: Laszlo Ersek <lersek at redhat.com>
Date: Tue, 18 Oct 2011 22:42:59 +0200
Subject: [PATCH] xen/time: remove blocked time accounting from xen "clockchip"

commit 0b0c002c340e78173789f8afaa508070d838cf3d upstream.

... because the "clock_event_device framework" already accounts for idle
time through the "event_handler" function pointer in
xen_timer_interrupt().

The patch is intended as the completion of [1]. It should fix the double
idle times seen in PV guests' /proc/stat [2]. It should be orthogonal to
stolen time accounting (the removed code seems to be isolated).

The approach may be completely misguided.

[1] https://lkml.org/lkml/2011/10/6/10
[2] http://lists.xensource.com/archives/html/xen-devel/2010-08/msg01068.html

John took the time to retest this patch on top of v3.10 and reported:
"idle time is correctly incremented for pv and hvm for the normal
case, nohz=off and nohz=idle." so lets put this patch in.

Signed-off-by: Laszlo Ersek <lersek at redhat.com>
Signed-off-by: John Haxby <john.haxby at oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 arch/x86/xen/time.c | 17 ++---------------
 1 file changed, 2 insertions(+), 15 deletions(-)

diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
index 054cc01..d50a821 100644
--- a/arch/x86/xen/time.c
+++ b/arch/x86/xen/time.c
@@ -36,9 +36,8 @@ static DEFINE_PER_CPU(struct vcpu_runstate_info, xen_runstate);
 /* snapshots of runstate info */
 static DEFINE_PER_CPU(struct vcpu_runstate_info, xen_runstate_snapshot);

-/* unused ns of stolen and blocked time */
+/* unused ns of stolen time */
 static DEFINE_PER_CPU(u64, xen_residual_stolen);
-static DEFINE_PER_CPU(u64, xen_residual_blocked);

 /* return an consistent snapshot of 64-bit time/counter value */
 static u64 get64(const u64 *p)
@@ -115,7 +114,7 @@ static void do_stolen_accounting(void)
 {
 	struct vcpu_runstate_info state;
 	struct vcpu_runstate_info *snap;
-	s64 blocked, runnable, offline, stolen;
+	s64 runnable, offline, stolen;
 	cputime_t ticks;

 	get_runstate_snapshot(&state);
@@ -125,7 +124,6 @@ static void do_stolen_accounting(void)
 	snap = &__get_cpu_var(xen_runstate_snapshot);

 	/* work out how much time the VCPU has not been runn*ing*  */
-	blocked = state.time[RUNSTATE_blocked] - snap->time[RUNSTATE_blocked];
 	runnable = state.time[RUNSTATE_runnable] - snap->time[RUNSTATE_runnable];
 	offline = state.time[RUNSTATE_offline] - snap->time[RUNSTATE_offline];

@@ -141,17 +139,6 @@ static void do_stolen_accounting(void)
 	ticks = iter_div_u64_rem(stolen, NS_PER_TICK, &stolen);
 	__this_cpu_write(xen_residual_stolen, stolen);
 	account_steal_ticks(ticks);
-
-	/* Add the appropriate number of ticks of blocked time,
-	   including any left-overs from last time. */
-	blocked += __this_cpu_read(xen_residual_blocked);
-
-	if (blocked < 0)
-		blocked = 0;
-
-	ticks = iter_div_u64_rem(blocked, NS_PER_TICK, &blocked);
-	__this_cpu_write(xen_residual_blocked, blocked);
-	account_idle_ticks(ticks);
 }

 /* Get the TSC speed from Xen */
--
1.8.1.2