[Xen-devel] [RFC PATCH 1/7] x86: improve psr scheduling code

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

From: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>

Switching RMID from previous vcpu to next vcpu only needs to write
MSR_IA32_PSR_ASSOC once. Write it with the value of next vcpu is enough,
no need to write '0' first. Idle domain has RMID set to 0 and because MSR
is already updated lazily, so just switch it as it does.

Also move the initialization of per-CPU variable which used for lazy
update from context switch to CPU starting.

Signed-off-by: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>
---
 xen/arch/x86/domain.c     |    7 +---
 xen/arch/x86/psr.c        |   89 +++++++++++++++++++++++++++++++++++----------
 xen/include/asm-x86/psr.h |    3 +-
 3 files changed, 73 insertions(+), 26 deletions(-)

diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index 393aa26..73f5d7f 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -1443,8 +1443,6 @@ static void __context_switch(void)
     {
         memcpy(&p->arch.user_regs, stack_regs, CTXT_SWITCH_STACK_BYTES);
         vcpu_save_fpu(p);
-        if ( psr_cmt_enabled() )
-            psr_assoc_rmid(0);
         p->arch.ctxt_switch_from(p);
     }
 
@@ -1469,11 +1467,10 @@ static void __context_switch(void)
         }
         vcpu_restore_fpu_eager(n);
         n->arch.ctxt_switch_to(n);
-
-        if ( psr_cmt_enabled() && n->domain->arch.psr_rmid > 0 )
-            psr_assoc_rmid(n->domain->arch.psr_rmid);
     }
 
+    psr_ctxt_switch_to(n->domain);
+
     gdt = !is_pv_32on64_vcpu(n) ? per_cpu(gdt_table, cpu) :
                                   per_cpu(compat_gdt_table, cpu);
     if ( need_full_gdt(n) )
diff --git a/xen/arch/x86/psr.c b/xen/arch/x86/psr.c
index 2ef83df..c902625 100644
--- a/xen/arch/x86/psr.c
+++ b/xen/arch/x86/psr.c
@@ -22,7 +22,6 @@
 
 struct psr_assoc {
     uint64_t val;
-    bool_t initialized;
 };
 
 struct psr_cmt *__read_mostly psr_cmt;
@@ -115,14 +114,6 @@ static void __init init_psr_cmt(unsigned int rmid_max)
     printk(XENLOG_INFO "Cache Monitoring Technology enabled\n");
 }
 
-static int __init init_psr(void)
-{
-    if ( (opt_psr & PSR_CMT) && opt_rmid_max )
-        init_psr_cmt(opt_rmid_max);
-    return 0;
-}
-__initcall(init_psr);
-
 /* Called with domain lock held, no psr specific lock needed */
 int psr_alloc_rmid(struct domain *d)
 {
@@ -168,26 +159,84 @@ void psr_free_rmid(struct domain *d)
     d->arch.psr_rmid = 0;
 }
 
-void psr_assoc_rmid(unsigned int rmid)
+static inline void psr_assoc_init(void)
 {
-    uint64_t val;
-    uint64_t new_val;
     struct psr_assoc *psra = &this_cpu(psr_assoc);
 
-    if ( !psra->initialized )
-    {
+    if ( psr_cmt_enabled() )
         rdmsrl(MSR_IA32_PSR_ASSOC, psra->val);
-        psra->initialized = 1;
+}
+
+static inline void psr_assoc_reg_read(struct psr_assoc *psra, uint64_t *reg)
+{
+    *reg = psra->val;
+}
+
+static inline void psr_assoc_reg_write(struct psr_assoc *psra, uint64_t reg)
+{
+    if ( reg != psra->val )
+    {
+        wrmsrl(MSR_IA32_PSR_ASSOC, reg);
+        psra->val = reg;
     }
-    val = psra->val;
+}
+
+static inline void psr_assoc_rmid(uint64_t *reg, unsigned int rmid)
+{
+    *reg = (*reg & ~rmid_mask) | (rmid & rmid_mask);
+}
+
+void psr_ctxt_switch_to(struct domain *d)
+{
+    uint64_t reg;
+    struct psr_assoc *psra = &this_cpu(psr_assoc);
+
+    psr_assoc_reg_read(psra, &reg);
 
-    new_val = (val & ~rmid_mask) | (rmid & rmid_mask);
-    if ( val != new_val )
+    if ( psr_cmt_enabled() )
+        psr_assoc_rmid(&reg, d->arch.psr_rmid);
+
+    psr_assoc_reg_write(psra, reg);
+}
+
+static void psr_cpu_init(unsigned int cpu)
+{
+    psr_assoc_init();
+}
+
+static int cpu_callback(
+    struct notifier_block *nfb, unsigned long action, void *hcpu)
+{
+    unsigned int cpu = (unsigned long)hcpu;
+
+    switch ( action )
+    {
+    case CPU_STARTING:
+        psr_cpu_init(cpu);
+        break;
+    }
+
+    return NOTIFY_DONE;
+}
+
+static struct notifier_block cpu_nfb = {
+    .notifier_call = cpu_callback
+};
+
+static int __init psr_presmp_init(void)
+{
+    if ( (opt_psr & PSR_CMT) && opt_rmid_max )
+        init_psr_cmt(opt_rmid_max);
+
+    if (  psr_cmt_enabled() )
     {
-        wrmsrl(MSR_IA32_PSR_ASSOC, new_val);
-        psra->val = new_val;
+        psr_cpu_init(smp_processor_id());
+        register_cpu_notifier(&cpu_nfb);
     }
+
+    return 0;
 }
+presmp_initcall(psr_presmp_init);
 
 /*
  * Local variables:
diff --git a/xen/include/asm-x86/psr.h b/xen/include/asm-x86/psr.h
index c6076e9..585350c 100644
--- a/xen/include/asm-x86/psr.h
+++ b/xen/include/asm-x86/psr.h
@@ -46,7 +46,8 @@ static inline bool_t psr_cmt_enabled(void)
 
 int psr_alloc_rmid(struct domain *d);
 void psr_free_rmid(struct domain *d);
-void psr_assoc_rmid(unsigned int rmid);
+
+void psr_ctxt_switch_to(struct domain *d);
 
 #endif /* __ASM_PSR_H__ */
 


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