Re: [PATCH] x86 linux: prevent halted VCPUs from eating up CPU bandwidth

["Jan Beulich" <jbeulich@novell.com>]

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>>> Keir Fraser <Keir.Fraser@cl.cam.ac.uk> 29.05.06 16:59 >>>
>
>On 29 May 2006, at 15:35, Jan Beulich wrote:
>
>> Since there was no reply to an earlier inquiry regarding this, here's 
>> a patch.
>>
>> Signed-off-by: Jan Beulich <jbeulich@novell.com>
>
>safe_halt() should simply be HYPERVISOR_block() -- the hypercall 
>implicitly reenables interrupt delivery for the calling VCPU, so no 
>need to call __sti() explicitly.
>
>halt() is a bit trickier -- given that it is executed (as far as I can 
>tell) only in contexts where the CPU has reached "end of life" (it's 
>crashed, or offlined, or shut down for some other reason) it might make 
>sense to define halt() as VCPUOP_down. Or, just in case it is used in 
>places with interrupts still enabled, where the CPU may have a future:
>#define halt() (irqs_disabled() ? HYPERVISOR_vcpu_op(VCPUOP_down) : 
>HYPERVISOR_block())

Indeed, this was the behavior I intended, but somehow I failed to find the VCPUOP_down operation that I was looking
for. Here's an updated patch.

Jan

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Index: head-2006-05-26/include/asm-i386/bugs.h
===================================================================
--- head-2006-05-26.orig/include/asm-i386/bugs.h	2006-03-20 06:53:29.000000000 +0100
+++ head-2006-05-26/include/asm-i386/bugs.h	2006-05-26 13:55:43.000000000 +0200
@@ -92,6 +92,7 @@ static void __init check_fpu(void)
 
 static void __init check_hlt(void)
 {
+#ifndef CONFIG_XEN
 	printk(KERN_INFO "Checking 'hlt' instruction... ");
 	if (!boot_cpu_data.hlt_works_ok) {
 		printk("disabled\n");
@@ -102,6 +103,7 @@ static void __init check_hlt(void)
 	halt();
 	halt();
 	printk("OK.\n");
+#endif
 }
 
 /*
Index: head-2006-05-26/include/asm-i386/mach-xen/asm/hypervisor.h
===================================================================
--- head-2006-05-26.orig/include/asm-i386/mach-xen/asm/hypervisor.h	2006-04-24 11:43:43.000000000 +0200
+++ head-2006-05-26/include/asm-i386/mach-xen/asm/hypervisor.h	2006-05-29 17:37:01.000000000 +0200
@@ -43,6 +43,7 @@
 #include <xen/interface/event_channel.h>
 #include <xen/interface/physdev.h>
 #include <xen/interface/sched.h>
+#include <xen/interface/vcpu.h>
 #include <xen/interface/nmi.h>
 #include <asm/ptrace.h>
 #include <asm/page.h>
Index: head-2006-05-26/include/asm-i386/mach-xen/asm/system.h
===================================================================
--- head-2006-05-26.orig/include/asm-i386/mach-xen/asm/system.h	2006-05-29 17:21:52.000000000 +0200
+++ head-2006-05-26/include/asm-i386/mach-xen/asm/system.h	2006-05-29 17:37:31.000000000 +0200
@@ -625,8 +625,11 @@ do {									\
 		preempt_enable_no_resched();				\
 } while (0)
 
-#define safe_halt()		((void)0)
-#define halt()			((void)0)
+#define safe_halt()		((void)HYPERVISOR_block())
+#define halt()			((void)					\
+	(HYPERVISOR_shared_info->vcpu_info[__vcpu_id].evtchn_upcall_mask \
+	 ? HYPERVISOR_vcpu_op(VCPUOP_down, __vcpu_id, NULL)		\
+	 : HYPERVISOR_block()))
 
 #define __save_and_cli(x)						\
 do {									\
Index: head-2006-05-26/include/asm-x86_64/mach-xen/asm/system.h
===================================================================
--- head-2006-05-26.orig/include/asm-x86_64/mach-xen/asm/system.h	2006-05-29 17:21:52.000000000 +0200
+++ head-2006-05-26/include/asm-x86_64/mach-xen/asm/system.h	2006-05-29 17:37:46.000000000 +0200
@@ -424,8 +424,11 @@ do {									\
 	preempt_enable_no_resched();					\
 	___x; })
 
-#define safe_halt()		((void)0)
-#define halt()			((void)0)
+#define safe_halt()		((void)HYPERVISOR_block())
+#define halt()			((void)					\
+	(HYPERVISOR_shared_info->vcpu_info[__vcpu_id].evtchn_upcall_mask \
+	 ? HYPERVISOR_vcpu_op(VCPUOP_down, __vcpu_id, NULL)		\
+	 : HYPERVISOR_block()))
 
 void cpu_idle_wait(void);
 

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