[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v4] x86/apicv: fix RTC periodic timer and apicv issue
Hi, xuquan. I have tested it on my skylake server. W/o this patch the inaccurate wall clock time issue only exists in Win7-32 guest. Win7-64, Win8-32, Win8-64, Win10-32 ,Win10-64 and linux-4.8.0+ guests don't have this issue. W/ this v4 patch, the issue disappears in Win7-32 guest and no wall lock time related regression is found on Win7-64, Win8-32, Win8-64, Win10-32, Win10-64 and linux-4.8.0+ guest. In windows guest, the test procedure is 1. Create a windows guest with 2 vCPU 2. run the following .bat in guest :abcd echo 111111 goto abcd 3. Start a stop-watch outside the guest and monitor the clock at the lower right corner in guest. After 120 seconds according the guest clock, stop the stop-watch. If the time shows in the stop-watch is about 120 seconds, then I think there is no the above issue in the guest. Otherwise, the time is inaccurate. In Win7-32 case, the stop-watch time is about 70 seconds, so the clock in guest is obviously inaccurate. In linux guest, the test procedure is 1. Create a linux guest with 4 vCPU 2. insmod the following linux module (through output of /proc/interrupt, about 850000 ipis in 13 seconds) 3. use date command to get guest time, others are same as test in windows guest #include <linux/init.h> #include <linux/module.h> #include <linux/kthread.h> #include <linux/sched.h> #include <asm/delay.h> MODULE_LICENSE("GPL"); void workload(void *info) { asm volatile("nop"); } void msleep(unsigned int msecs); static int ipi_generator(void * info) { int i; while (!kthread_should_stop()) { for(i=0; i< 5 * 10000; i++) { smp_call_function(workload, NULL,1); } msleep(1); } return 0; } struct task_struct *thread; static int __init ipi_init(void) { thread = kthread_run(ipi_generator, NULL, "IPI"); if (IS_ERR(thread)) return PTR_ERR(thread); return 0; } static void __exit ipi_exit(void) { kthread_stop(thread); } module_init(ipi_init); module_exit(ipi_exit); Are these tests sufficient? Please let me know if you have any other thoughts. On Wed, Dec 21, 2016 at 05:44:08AM +0000, Xuquan (Quan Xu) wrote: >When Xen apicv is enabled, wall clock time is faster on Windows7-32 >guest with high payload (with 2vCPU, captured from xentrace, in >high payload, the count of IPI interrupt increases rapidly between >these vCPUs). > >If IPI intrrupt (vector 0xe1) and periodic timer interrupt (vector 0xd1) >are both pending (index of bit set in vIRR), unfortunately, the IPI >intrrupt is high priority than periodic timer interrupt. Xen updates >IPI interrupt bit set in vIRR to guest interrupt status (RVI) as a high >priority and apicv (Virtual-Interrupt Delivery) delivers IPI interrupt >within VMX non-root operation without a VM-Exit. Within VMX non-root >operation, if periodic timer interrupt index of bit is set in vIRR and >highest, the apicv delivers periodic timer interrupt within VMX non-root >operation as well. > >But in current code, if Xen doesn't update periodic timer interrupt bit >set in vIRR to guest interrupt status (RVI) directly, Xen is not aware >of this case to decrease the count (pending_intr_nr) of pending periodic >timer interrupt, then Xen will deliver a periodic timer interrupt again. > >And that we update periodic timer interrupt in every VM-entry, there is >a chance that already-injected instance (before EOI-induced exit happens) >will incur another pending IRR setting if there is a VM-exit happens >between virtual interrupt injection (vIRR->0, vISR->1) and EOI-induced >exit (vISR->0), since pt_intr_post hasn't been invoked yet, then the >guest receives more periodic timer interrupt. > >So we set eoi_exit_bitmap for intack.vector when it's higher than >pending periodic time interrupts. This way we can guarantee there's >always a chance to post periodic time interrupts when periodic time >interrupts becomes the highest one. > >Signed-off-by: Quan Xu <xuquan8@xxxxxxxxxx> >--- > xen/arch/x86/hvm/vmx/intr.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > >diff --git a/xen/arch/x86/hvm/vmx/intr.c b/xen/arch/x86/hvm/vmx/intr.c >index 639a705..0cf26b4 100644 >--- a/xen/arch/x86/hvm/vmx/intr.c >+++ b/xen/arch/x86/hvm/vmx/intr.c >@@ -315,9 +315,13 @@ void vmx_intr_assist(void) > * Set eoi_exit_bitmap for periodic timer interrup to cause > EOI-induced VM > * exit, then pending periodic time interrups have the chance to be > injected > * for compensation >+ * Set eoi_exit_bitmap for intack.vector when it's higher than pending >+ * periodic time interrupts. This way we can guarantee there's always >a chance >+ * to post periodic time interrupts when periodic time interrupts >becomes the >+ * highest one > */ > if (pt_vector != -1) >- vmx_set_eoi_exit_bitmap(v, pt_vector); >+ vmx_set_eoi_exit_bitmap(v, intack.vector); > > /* we need update the RVI field */ > __vmread(GUEST_INTR_STATUS, &status); >@@ -334,7 +338,8 @@ void vmx_intr_assist(void) > __vmwrite(EOI_EXIT_BITMAP(i), v->arch.hvm_vmx.eoi_exit_bitmap[i]); > } > >- pt_intr_post(v, intack); >+ if ( intack.vector == pt_vector ) >+ pt_intr_post(v, intack); > } > else > { >-- >1.8.3.4 _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel
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