[xen staging] viridian: use softirq batching in hvcall_ipi()

[patchbot@xxxxxxx]

commit 3a3f4f00afcdcf2cdae47319168b8dadab41c4f4
Author:     Paul Durrant <pdurrant@xxxxxxxxxx>
AuthorDate: Fri Dec 4 13:14:42 2020 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri Dec 4 13:14:42 2020 +0100

    viridian: use softirq batching in hvcall_ipi()
    
    vlapic_ipi() uses a softirq batching mechanism to improve the efficiency of
    sending a IPIs to large number of processors. This patch modifies send_ipi()
    (the worker function called by hvcall_ipi()) to also make use of the
    mechanism when there multiple bits set the hypercall_vpmask.
    
    Signed-off-by: Paul Durrant <pdurrant@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Wei Liu <wl@xxxxxxx>
---
 xen/arch/x86/hvm/viridian/viridian.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/xen/arch/x86/hvm/viridian/viridian.c 
b/xen/arch/x86/hvm/viridian/viridian.c
index 3e2393be41..894946abcb 100644
--- a/xen/arch/x86/hvm/viridian/viridian.c
+++ b/xen/arch/x86/hvm/viridian/viridian.c
@@ -11,6 +11,7 @@
 #include <xen/hypercall.h>
 #include <xen/domain_page.h>
 #include <xen/param.h>
+#include <xen/softirq.h>
 #include <asm/guest/hyperv-tlfs.h>
 #include <asm/paging.h>
 #include <asm/p2m.h>
@@ -571,6 +572,11 @@ static unsigned int vpmask_next(const struct 
hypercall_vpmask *vpmask,
              (vp) < HVM_MAX_VCPUS; \
              (vp) = vpmask_next(vpmask, vp) )
 
+static unsigned int vpmask_nr(const struct hypercall_vpmask *vpmask)
+{
+    return bitmap_weight(vpmask->mask, HVM_MAX_VCPUS);
+}
+
 /*
  * Windows should not issue the hypercalls requiring this callback in the
  * case where vcpu_id would exceed the size of the mask.
@@ -654,10 +660,17 @@ static int hvcall_flush(const union hypercall_input 
*input,
 static void send_ipi(struct hypercall_vpmask *vpmask, uint8_t vector)
 {
     struct domain *currd = current->domain;
+    unsigned int nr = vpmask_nr(vpmask);
     unsigned int vp;
 
+    if ( nr > 1 )
+        cpu_raise_softirq_batch_begin();
+
     for_each_vp ( vpmask, vp )
         vlapic_set_irq(vcpu_vlapic(currd->vcpu[vp]), vector, 0);
+
+    if ( nr > 1 )
+        cpu_raise_softirq_batch_finish();
 }
 
 static int hvcall_ipi(const union hypercall_input *input,
--
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