[PATCH 05/10] viridian: use softirq batching in hvcall_ipi()

[Paul Durrant <paul@xen.org>]

From: Paul Durrant <pdurrant@amazon.com>

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. Hence a `nr`
field is added to the structure to track the number of set bits.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
---
Cc: Wei Liu <wl@xen.org>
Cc: Jan Beulich <jbeulich@suse.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: "Roger Pau Monné" <roger.pau@citrix.com>
---
 xen/arch/x86/hvm/viridian/viridian.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/hvm/viridian/viridian.c b/xen/arch/x86/hvm/viridian/viridian.c
index 63f63093a513..765d53016c02 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>
@@ -509,6 +510,7 @@ void viridian_domain_deinit(struct domain *d)
 
 struct hypercall_vpmask {
     DECLARE_BITMAP(mask, HVM_MAX_VCPUS);
+    unsigned int nr;
 };
 
 static DEFINE_PER_CPU(struct hypercall_vpmask, hypercall_vpmask);
@@ -516,21 +518,24 @@ static DEFINE_PER_CPU(struct hypercall_vpmask, hypercall_vpmask);
 static void vpmask_empty(struct hypercall_vpmask *vpmask)
 {
     bitmap_zero(vpmask->mask, HVM_MAX_VCPUS);
+    vpmask->nr = 0;
 }
 
 static void vpmask_set(struct hypercall_vpmask *vpmask, unsigned int vp)
 {
-    __set_bit(vp, vpmask->mask);
+    if ( !test_and_set_bit(vp, vpmask->mask) )
+        vpmask->nr++;
 }
 
 static void vpmask_fill(struct hypercall_vpmask *vpmask)
 {
     bitmap_fill(vpmask->mask, HVM_MAX_VCPUS);
+    vpmask->nr = HVM_MAX_VCPUS;
 }
 
 static bool vpmask_test(struct hypercall_vpmask *vpmask, unsigned int vp)
 {
-    return test_bit(vp, vpmask->mask);
+    return vpmask->nr && test_bit(vp, vpmask->mask);
 }
 
 static unsigned int vpmask_first(struct hypercall_vpmask *vpmask)
@@ -644,8 +649,17 @@ static void send_ipi(struct hypercall_vpmask *vpmask, uint8_t vector)
     struct domain *currd = current->domain;
     unsigned int vp;
 
+    if ( !vpmask->nr )
+        return;
+
+    if ( vpmask->nr > 1 )
+        cpu_raise_softirq_batch_begin();
+
     for_each_vp ( vpmask, vp )
         vlapic_set_irq(vcpu_vlapic(currd->vcpu[vp]), vector, 0);
+
+    if ( vpmask->nr > 1 )
+        cpu_raise_softirq_batch_finish();
 }
 
 static int hvcall_ipi(union hypercall_input *input,
-- 
2.20.1