[Xen-changelog] [xen master] x86: avoid flush IPI when possible

[patchbot@xxxxxxx]

commit 216a082b10a7c0e40757a6aad075e0cb4f080c7b
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Thu Feb 18 15:02:16 2016 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Feb 18 15:02:16 2016 +0100

    x86: avoid flush IPI when possible
    
    Since CLFLUSH, other than WBINVD, is a cache coherency domain wide
    flush, there's no need to IPI other CPUs if this is the only flushing
    being requested. (As a secondary change, move a local variable into the
    scope where it's actually needed.)
    
    As a secondary change also eliminate another leftover from 32-bit days:
    invalidate_interrupt() can clear FLUSH_TLB_GLOBAL alongside FLUSH_TLB,
    since write_ptbase() (as a descendant of __sync_local_execstate()) now
    unconditionally fiddles with CR4.PGE.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 xen/arch/x86/flushtlb.c        | 12 ++++++++++--
 xen/arch/x86/smp.c             | 18 +++++++++++-------
 xen/include/asm-x86/flushtlb.h |  2 +-
 3 files changed, 22 insertions(+), 10 deletions(-)

diff --git a/xen/arch/x86/flushtlb.c b/xen/arch/x86/flushtlb.c
index 961bb1d..582a1e2 100644
--- a/xen/arch/x86/flushtlb.c
+++ b/xen/arch/x86/flushtlb.c
@@ -91,9 +91,13 @@ void write_cr3(unsigned long cr3)
     local_irq_restore(flags);
 }
 
-void flush_area_local(const void *va, unsigned int flags)
+/*
+ * The return value of this function is the passed in "flags" argument with
+ * bits cleared that have been fully (i.e. system-wide) taken care of, i.e.
+ * namely not requiring any further action on remote CPUs.
+ */
+unsigned int flush_area_local(const void *va, unsigned int flags)
 {
-    const struct cpuinfo_x86 *c = &current_cpu_data;
     unsigned int order = (flags - 1) & FLUSH_ORDER_MASK;
     unsigned long irqfl;
 
@@ -130,6 +134,7 @@ void flush_area_local(const void *va, unsigned int flags)
 
     if ( flags & FLUSH_CACHE )
     {
+        const struct cpuinfo_x86 *c = &current_cpu_data;
         unsigned long i, sz = 0;
 
         if ( order < (BITS_PER_LONG - PAGE_SHIFT) )
@@ -146,6 +151,7 @@ void flush_area_local(const void *va, unsigned int flags)
                                   "data16 clflush %0",      /* clflushopt */
                                   X86_FEATURE_CLFLUSHOPT,
                                   "m" (((const char *)va)[i]));
+            flags &= ~FLUSH_CACHE;
         }
         else
         {
@@ -154,4 +160,6 @@ void flush_area_local(const void *va, unsigned int flags)
     }
 
     local_irq_restore(irqfl);
+
+    return flags;
 }
diff --git a/xen/arch/x86/smp.c b/xen/arch/x86/smp.c
index 988b9c2..4abb16f 100644
--- a/xen/arch/x86/smp.c
+++ b/xen/arch/x86/smp.c
@@ -205,26 +205,30 @@ static unsigned int flush_flags;
 
 void invalidate_interrupt(struct cpu_user_regs *regs)
 {
+    unsigned int flags = flush_flags;
     ack_APIC_irq();
     perfc_incr(ipis);
-    if ( !__sync_local_execstate() ||
-         (flush_flags & (FLUSH_TLB_GLOBAL | FLUSH_CACHE)) )
-        flush_area_local(flush_va, flush_flags);
+    if ( __sync_local_execstate() )
+        flags &= ~(FLUSH_TLB | FLUSH_TLB_GLOBAL);
+    flush_area_local(flush_va, flags);
     cpumask_clear_cpu(smp_processor_id(), &flush_cpumask);
 }
 
 void flush_area_mask(const cpumask_t *mask, const void *va, unsigned int flags)
 {
+    unsigned int cpu = smp_processor_id();
+
     ASSERT(local_irq_is_enabled());
 
-    if ( cpumask_test_cpu(smp_processor_id(), mask) )
-        flush_area_local(va, flags);
+    if ( cpumask_test_cpu(cpu, mask) )
+        flags = flush_area_local(va, flags);
 
-    if ( !cpumask_subset(mask, cpumask_of(smp_processor_id())) )
+    if ( (flags & ~FLUSH_ORDER_MASK) &&
+         !cpumask_subset(mask, cpumask_of(cpu)) )
     {
         spin_lock(&flush_lock);
         cpumask_and(&flush_cpumask, mask, &cpu_online_map);
-        cpumask_clear_cpu(smp_processor_id(), &flush_cpumask);
+        cpumask_clear_cpu(cpu, &flush_cpumask);
         flush_va      = va;
         flush_flags   = flags;
         send_IPI_mask(&flush_cpumask, INVALIDATE_TLB_VECTOR);
diff --git a/xen/include/asm-x86/flushtlb.h b/xen/include/asm-x86/flushtlb.h
index 8dbe2d6..4ea31c2 100644
--- a/xen/include/asm-x86/flushtlb.h
+++ b/xen/include/asm-x86/flushtlb.h
@@ -87,7 +87,7 @@ void write_cr3(unsigned long cr3);
 #define FLUSH_CACHE      0x400
 
 /* Flush local TLBs/caches. */
-void flush_area_local(const void *va, unsigned int flags);
+unsigned int flush_area_local(const void *va, unsigned int flags);
 #define flush_local(flags) flush_area_local(NULL, flags)
 
 /* Flush specified CPUs' TLBs/caches */
--
generated by git-patchbot for /home/xen/git/xen.git#master

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