WARNING - OLD ARCHIVES

This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
   
 
 
Xen 
 
Home Products Support Community News
 
   
 

xen-devel

[Xen-devel] [PATCH 3/3] kvm guest : Add support for pv-ticketlocks

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: [Xen-devel] [PATCH 3/3] kvm guest : Add support for pv-ticketlocks
From: Srivatsa Vaddagiri <vatsa@xxxxxxxxxxxxxxxxxx>
Date: Wed, 19 Jan 2011 22:47:57 +0530
Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>, Nick Piggin <npiggin@xxxxxxxxx>, kvm@xxxxxxxxxxxxxxx, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxxxx>, Eric Dumazet <dada1@xxxxxxxxxxxxx>, Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>, suzuki@xxxxxxxxxx, Avi Kivity <avi@xxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, Américo Wang <xiyou.wangcong@xxxxxxxxx>, Linux Virtualization <virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx>
Delivery-date: Wed, 19 Jan 2011 09:34:02 -0800
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <20110119164432.GA30669@xxxxxxxxxxxxxxxxxx>
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
References: <cover.1289940821.git.jeremy.fitzhardinge@xxxxxxxxxx> <20110119164432.GA30669@xxxxxxxxxxxxxxxxxx>
Reply-to: vatsa@xxxxxxxxxxxxxxxxxx
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
User-agent: Mutt/1.5.20 (2009-06-14)
This patch extends Linux guests running on KVM hypervisor to support
pv-ticketlocks. Very early during bootup, paravirtualied KVM guest detects if 
the hypervisor has required feature (KVM_FEATURE_WAIT_FOR_KICK) to support 
pv-ticketlocks. If so, support for pv-ticketlocks is registered via pv_lock_ops.

Signed-off-by: Srivatsa Vaddagiri <vatsa@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Suzuki Poulose <suzuki@xxxxxxxxxx>

---
 arch/x86/Kconfig                |    9 +
 arch/x86/include/asm/kvm_para.h |    8 +
 arch/x86/kernel/head64.c        |    3 
 arch/x86/kernel/kvm.c           |  208 ++++++++++++++++++++++++++++++++++++++++
 4 files changed, 228 insertions(+)

Index: linux-2.6.37/arch/x86/Kconfig
===================================================================
--- linux-2.6.37.orig/arch/x86/Kconfig
+++ linux-2.6.37/arch/x86/Kconfig
@@ -508,6 +508,15 @@ config KVM_GUEST
          This option enables various optimizations for running under the KVM
          hypervisor.
 
+config KVM_DEBUG_FS
+       bool "Enable debug information for KVM Guests in debugfs"
+       depends on KVM_GUEST
+       default n
+       ---help---
+         This option enables collection of various statistics for KVM guest.
+         Statistics are displayed in debugfs filesystem. Enabling this option
+         may incur significant overhead.
+
 source "arch/x86/lguest/Kconfig"
 
 config PARAVIRT
Index: linux-2.6.37/arch/x86/include/asm/kvm_para.h
===================================================================
--- linux-2.6.37.orig/arch/x86/include/asm/kvm_para.h
+++ linux-2.6.37/arch/x86/include/asm/kvm_para.h
@@ -162,8 +162,16 @@ static inline unsigned int kvm_arch_para
 
 #ifdef CONFIG_KVM_GUEST
 void __init kvm_guest_init(void);
+
+#ifdef CONFIG_PARAVIRT_SPINLOCKS
+void __init kvm_guest_early_init(void);
+#else
+#define kvm_guest_early_init() do { } while (0)
+#endif
+
 #else
 #define kvm_guest_init() do { } while (0)
+#define kvm_guest_early_init() do { } while (0)
 #endif
 
 #endif /* __KERNEL__ */
Index: linux-2.6.37/arch/x86/kernel/head64.c
===================================================================
--- linux-2.6.37.orig/arch/x86/kernel/head64.c
+++ linux-2.6.37/arch/x86/kernel/head64.c
@@ -13,6 +13,7 @@
 #include <linux/start_kernel.h>
 #include <linux/io.h>
 #include <linux/memblock.h>
+#include <linux/kvm_para.h>
 
 #include <asm/processor.h>
 #include <asm/proto.h>
@@ -118,6 +119,8 @@ void __init x86_64_start_reservations(ch
 
        reserve_ebda_region();
 
+       kvm_guest_early_init();
+
        /*
         * At this point everything still needed from the boot loader
         * or BIOS or kernel text should be early reserved or marked not
Index: linux-2.6.37/arch/x86/kernel/kvm.c
===================================================================
--- linux-2.6.37.orig/arch/x86/kernel/kvm.c
+++ linux-2.6.37/arch/x86/kernel/kvm.c
@@ -238,3 +238,211 @@ void __init kvm_guest_init(void)
 
        paravirt_ops_setup();
 }
+
+#ifdef CONFIG_PARAVIRT_SPINLOCKS
+
+#ifdef CONFIG_KVM_DEBUG_FS
+
+#include <linux/debugfs.h>
+#include <linux/sched.h>
+
+static struct kvm_spinlock_stats
+{
+       u32 taken_slow;
+       u32 taken_slow_pickup;
+
+       u32 released_slow;
+       u32 released_slow_kicked;
+
+#define HISTO_BUCKETS  30
+       u32 histo_spin_blocked[HISTO_BUCKETS+1];
+
+       u64 time_blocked;
+} spinlock_stats;
+
+static u8 zero_stats;
+
+static inline void check_zero(void)
+{
+       if (unlikely(zero_stats)) {
+               memset(&spinlock_stats, 0, sizeof(spinlock_stats));
+               zero_stats = 0;
+       }
+}
+
+#define ADD_STATS(elem, val)                   \
+       do { check_zero(); spinlock_stats.elem += (val); } while (0)
+
+static inline u64 spin_time_start(void)
+{
+       return sched_clock();
+}
+
+static void __spin_time_accum(u64 delta, u32 *array)
+{
+       unsigned index = ilog2(delta);
+
+       check_zero();
+
+       if (index < HISTO_BUCKETS)
+               array[index]++;
+       else
+               array[HISTO_BUCKETS]++;
+}
+
+static inline void spin_time_accum_blocked(u64 start)
+{
+       u32 delta = sched_clock() - start;
+
+       __spin_time_accum(delta, spinlock_stats.histo_spin_blocked);
+       spinlock_stats.time_blocked += delta;
+}
+
+static struct dentry *d_spin_debug;
+static struct dentry *d_kvm_debug;
+
+struct dentry *kvm_init_debugfs(void)
+{
+       d_kvm_debug = debugfs_create_dir("kvm", NULL);
+       if (!d_kvm_debug)
+               printk(KERN_WARNING "Could not create 'kvm' debugfs 
directory\n");
+
+       return d_kvm_debug;
+}
+
+static int __init kvm_spinlock_debugfs(void)
+{
+       struct dentry *d_kvm = kvm_init_debugfs();
+
+       if (d_kvm == NULL)
+               return -ENOMEM;
+
+       d_spin_debug = debugfs_create_dir("spinlocks", d_kvm);
+
+       debugfs_create_u8("zero_stats", 0644, d_spin_debug, &zero_stats);
+
+       debugfs_create_u32("taken_slow", 0444, d_spin_debug,
+                          &spinlock_stats.taken_slow);
+       debugfs_create_u32("taken_slow_pickup", 0444, d_spin_debug,
+                          &spinlock_stats.taken_slow_pickup);
+
+       debugfs_create_u32("released_slow", 0444, d_spin_debug,
+                          &spinlock_stats.released_slow);
+       debugfs_create_u32("released_slow_kicked", 0444, d_spin_debug,
+                          &spinlock_stats.released_slow_kicked);
+
+       debugfs_create_u64("time_blocked", 0444, d_spin_debug,
+                          &spinlock_stats.time_blocked);
+
+       debugfs_create_u32_array("histo_blocked", 0444, d_spin_debug,
+                    spinlock_stats.histo_spin_blocked, HISTO_BUCKETS + 1);
+
+       return 0;
+}
+fs_initcall(kvm_spinlock_debugfs);
+#else  /* !CONFIG_KVM_DEBUG_FS */
+#define TIMEOUT                        (1 << 10)
+#define ADD_STATS(elem, val)   do { (void)(val); } while (0)
+
+static inline u64 spin_time_start(void)
+{
+       return 0;
+}
+
+static inline void spin_time_accum_blocked(u64 start)
+{
+}
+#endif  /* CONFIG_KVM_DEBUG_FS */
+
+struct kvm_lock_waiting {
+       struct arch_spinlock *lock;
+       __ticket_t want;
+};
+
+/* cpus 'waiting' on a spinlock to become available */
+static cpumask_t waiting_cpus;
+
+/* Track spinlock on which a cpu is waiting */
+static DEFINE_PER_CPU(struct kvm_lock_waiting, lock_waiting);
+
+static inline void kvm_wait_for_kick(void)
+{
+       kvm_hypercall0(KVM_HC_WAIT_FOR_KICK);
+}
+
+static void kvm_lock_spinning(struct arch_spinlock *lock, unsigned want)
+{
+       struct kvm_lock_waiting *w = &__get_cpu_var(lock_waiting);
+       int cpu = smp_processor_id();
+       u64 start;
+
+       start = spin_time_start();
+
+       w->want = want;
+       w->lock = lock;
+
+       ADD_STATS(taken_slow, 1);
+
+       cpumask_set_cpu(cpu, &waiting_cpus);
+
+       /* Mark entry to slowpath before doing the pickup test to make
+          sure we don't deadlock with an unlocker. */
+       __ticket_enter_slowpath(lock);
+
+       /* check again make sure it didn't become free while
+          we weren't looking  */
+       if (ACCESS_ONCE(lock->tickets.head) == want) {
+               ADD_STATS(taken_slow_pickup, 1);
+               goto out;
+       }
+
+       kvm_wait_for_kick();
+
+out:
+       cpumask_clear_cpu(cpu, &waiting_cpus);
+       w->lock = NULL;
+       spin_time_accum_blocked(start);
+}
+PV_CALLEE_SAVE_REGS_THUNK(kvm_lock_spinning);
+
+/* Kick a cpu */
+static inline void kvm_kick_cpu(int cpu)
+{
+       kvm_hypercall1(KVM_HC_KICK_CPU, cpu);
+}
+
+/* Kick vcpu waiting on @lock->head to reach value @ticket */
+static void kvm_unlock_kick(struct arch_spinlock *lock, unsigned ticket)
+{
+       int cpu;
+
+       ADD_STATS(released_slow, 1);
+
+       for_each_cpu(cpu, &waiting_cpus) {
+               const struct kvm_lock_waiting *w = &per_cpu(lock_waiting, cpu);
+               if (w->lock == lock && w->want == ticket) {
+                       ADD_STATS(released_slow_kicked, 1);
+                       kvm_kick_cpu(cpu);
+                       break;
+               }
+       }
+}
+
+/*
+ * Setup pv_lock_ops to exploit KVM_FEATURE_WAIT_FOR_KICK if present.
+ * This needs to be setup really early in boot, before the first call to
+ * spinlock is issued!
+ */
+void __init kvm_guest_early_init(void)
+{
+       if (!kvm_para_available())
+               return;
+
+       /* Does host kernel support KVM_FEATURE_WAIT_FOR_KICK? */
+       if (!kvm_para_has_feature(KVM_FEATURE_WAIT_FOR_KICK))
+               return;
+
+       pv_lock_ops.lock_spinning = PV_CALLEE_SAVE(kvm_lock_spinning);
+       pv_lock_ops.unlock_kick = kvm_unlock_kick;
+}
+#endif /* CONFIG_PARAVIRT_SPINLOCKS */

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel