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Re: [Xen-devel] [PATCH 2/4] xen: Add 'synthetic' preemption check parameter
Hi George,
I was expecting a bigger list of CC here. What did you use to compute it? In order to better test hypervisor preemption paths, add an option to
artificially increase the number of preemptions.
While modifying xen-command-line.pandoc, escape some underscores, and
remove some trailing whitespace.
Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxx>
---
CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CC: Jan Beulich <jbeulich@xxxxxxxx>
---
docs/misc/xen-command-line.pandoc | 20 ++++++++++++++++++--
xen/arch/x86/time.c | 11 +++++++++++
xen/include/xen/sched.h | 10 +++++++++-
3 files changed, 38 insertions(+), 3 deletions(-)
diff --git a/docs/misc/xen-command-line.pandoc b/docs/misc/xen-command-line.pandoc
index 981a5e2381..1a9fda8627 100644
--- a/docs/misc/xen-command-line.pandoc
+++ b/docs/misc/xen-command-line.pandoc
@@ -636,13 +636,29 @@ Available alternatives, with their meaning, are:
Specify the USB controller to use, either by instance number (when going
over the PCI busses sequentially) or by PCI device (must be on segment 0).
-### debug_stack_lines
+### debug\_stack\_lines
> `= <integer>`
> Default: `20`
Limits the number lines printed in Xen stack traces.
+### debug-synthetic-preemption
+> `= <integer>`
+
+> Default: `0`
+
+Artificially increases rate at which `hypercall_preempt_check()`
+returns `true`, for debugging purposes, to a rate of one in `N`. (The
+default, `0`, disables the feature.)
+
+When promoting pagetables, for instance, `hypercall_preempt_check()`
+is called before processing each PTE. Since there are 512 PTEs per
+page, a value of `1024` should result in pagetable promotion being
+interrupted every other page on average.
+
+Only available in DEBUG builds.
+
### debugtrace
> `= [cpu:]<size>`
@@ -1690,7 +1706,7 @@ The following resources are available:
CDP, one COS will corespond two CBMs other than one with CAT, due to the
sum of CBMs is fixed, that means actual `cos_max` in use will automatically
reduce to half when CDP is enabled.
-
+
### pv-linear-pt (x86)
> `= <boolean>`
diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c
index 64e471a39b..34302f81e7 100644
--- a/xen/arch/x86/time.c
+++ b/xen/arch/x86/time.c
@@ -43,6 +43,17 @@
static char __initdata opt_clocksource[10];
string_param("clocksource", opt_clocksource);
+#ifndef NDEBUG
+int debug_synthetic_preemption = 0;
+integer_param("debug-synthetic-preemption", debug_synthetic_preemption);
+
+bool synthetic_preemption_check(void) {
+ if ( debug_synthetic_preemption == 0 )
+ return false;
+ return !(rdtsc() % debug_synthetic_preemption);
+}
+#endif
+
unsigned long __read_mostly cpu_khz; /* CPU clock frequency in kHz. */
DEFINE_SPINLOCK(rtc_lock);
unsigned long pit0_ticks;
diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
index 9f7bc69293..c0071eee04 100644
--- a/xen/include/xen/sched.h
+++ b/xen/include/xen/sched.h
@@ -748,6 +748,13 @@ static inline void hypercall_cancel_continuation(struct vcpu *v)
v->hcall_preempted = false;
}
+#ifndef NDEBUG
+bool synthetic_preemption_check(void);
+#define synthetic_preemption_check synthetic_preemption_check
Why do you need this define?
+#else
+#define synthetic_preempiton_check() false
Typo in the name. Also, it seems like this wasn't tested on Arm and, AFAICT break because the function would not be definr in debug build.
But, I am not sure why the implementation needs to be arch specific when get_cycles() could do the job.
+#endif
+
/*
* For long-running operations that must be in hypercall context, check
* if there is background work to be done that should interrupt this
@@ -755,7 +762,8 @@ static inline void hypercall_cancel_continuation(struct vcpu *v)
*/
#define hypercall_preempt_check() (unlikely( \
softirq_pending(smp_processor_id()) | \
- local_events_need_delivery() \
+ local_events_need_delivery() | \
+ synthetic_preemption_check() \
The function you return bool, so shouldn't it be ||?
Cheers,
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