[Xen-changelog] [xen master] grant-table: defer releasing pages acquired in a grant copy

[patchbot@xxxxxxx]

commit d28f42f2703e483116bafd2b0b76a32af67d83ad
Author:     David Vrabel <david.vrabel@xxxxxxxxxx>
AuthorDate: Thu Jan 29 14:22:22 2015 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Jan 29 14:22:22 2015 +0100

    grant-table: defer releasing pages acquired in a grant copy
    
    Acquiring a page for the source or destination of a grant copy is an
    expensive operation.  A common use case is for two adjacent grant copy
    ops to operate on either the same source or the same destination page.
    
    Instead of always acquiring and releasing destination and source pages
    for each operation, release the page once it is no longer valid for
    the next op.
    
    If either the source or destination domains changes both pages are
    released as it is unlikely that either will still be valid.
    
    XenServer's performance benchmarks show modest improvements in network
    receive throughput (netback uses grant copy in the guest Rx path) and
    no regressions in disk performance (using tapdisk3 which grant copies
    as the backend).
    
                             Baseline   Deferred Release
    Interhost receive to VM   7.2 Gb/s  ~9 Gbit/s
    Interhost aggregate      24 Gb/s    28 Gb/s
    Intrahost single stream  14 Gb/s    14 Gb/s
    Intrahost aggregate      34 Gb/s    36 Gb/s
    Aggregate disk write    900 MB/s   900 MB/s
    Aggregate disk read     890 MB/s   890 MB/s
    
    Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
    Reviewed-by: Tim Deegan <tim@xxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/common/grant_table.c |   83 ++++++++++++++++++++++++++++++++++++---------
 1 files changed, 66 insertions(+), 17 deletions(-)

diff --git a/xen/common/grant_table.c b/xen/common/grant_table.c
index f5b25bc..e44fe20 100644
--- a/xen/common/grant_table.c
+++ b/xen/common/grant_table.c
@@ -2236,6 +2236,17 @@ static int gnttab_copy_claim_buf(const struct 
gnttab_copy *op,
     return rc;
 }
 
+static bool_t gnttab_copy_buf_valid(const struct gnttab_copy_ptr *p,
+                                    const struct gnttab_copy_buf *b,
+                                    bool_t has_gref)
+{
+    if ( !b->virt )
+        return 0;
+    if ( has_gref )
+        return b->have_grant && p->u.ref == b->ptr.u.ref;
+    return p->u.gmfn == b->ptr.u.gmfn;
+}
+
 static int gnttab_copy_buf(const struct gnttab_copy *op,
                            struct gnttab_copy_buf *dest,
                            const struct gnttab_copy_buf *src)
@@ -2274,23 +2285,40 @@ static int gnttab_copy_one(const struct gnttab_copy *op,
 {
     int rc;
 
-    rc = gnttab_copy_lock_domains(op, src, dest);
-    if ( rc < 0 )
-        goto out;
+    if ( !src->domain || op->source.domid != src->ptr.domid ||
+         !dest->domain || op->dest.domid != dest->ptr.domid )
+    {
+        gnttab_copy_release_buf(src);
+        gnttab_copy_release_buf(dest);
+        gnttab_copy_unlock_domains(src, dest);
 
-    rc = gnttab_copy_claim_buf(op, &op->source, src, GNTCOPY_source_gref);
-    if ( rc < 0 )
-        goto out;
+        rc = gnttab_copy_lock_domains(op, src, dest);
+        if ( rc < 0 )
+            goto out;
+    }
 
-    rc = gnttab_copy_claim_buf(op, &op->dest, dest, GNTCOPY_dest_gref);
-    if ( rc < 0 )
-        goto out;
+    /* Different source? */
+    if ( !gnttab_copy_buf_valid(&op->source, src,
+                                op->flags & GNTCOPY_source_gref) )
+    {
+        gnttab_copy_release_buf(src);
+        rc = gnttab_copy_claim_buf(op, &op->source, src, GNTCOPY_source_gref);
+        if ( rc < 0 )
+            goto out;
+    }
+
+    /* Different dest? */
+    if ( !gnttab_copy_buf_valid(&op->dest, dest,
+                                op->flags & GNTCOPY_dest_gref) )
+    {
+        gnttab_copy_release_buf(dest);
+        rc = gnttab_copy_claim_buf(op, &op->dest, dest, GNTCOPY_dest_gref);
+        if ( rc < 0 )
+            goto out;
+    }
 
     rc = gnttab_copy_buf(op, dest, src);
  out:
-    gnttab_copy_release_buf(src);
-    gnttab_copy_release_buf(dest);
-    gnttab_copy_unlock_domains(src, dest);
     return rc;
 }
 
@@ -2301,21 +2329,42 @@ static long gnttab_copy(
     struct gnttab_copy op;
     struct gnttab_copy_buf src = {};
     struct gnttab_copy_buf dest = {};
+    long rc = 0;
 
     for ( i = 0; i < count; i++ )
     {
-        if (i && hypercall_preempt_check())
-            return i;
+        if ( i && hypercall_preempt_check() )
+        {
+            rc = i;
+            break;
+        }
+
         if ( unlikely(__copy_from_guest(&op, uop, 1)) )
-            return -EFAULT;
+        {
+            rc = -EFAULT;
+            break;
+        }
 
         op.status = gnttab_copy_one(&op, &dest, &src);
+        if ( op.status != GNTST_okay )
+        {
+            gnttab_copy_release_buf(&src);
+            gnttab_copy_release_buf(&dest);
+        }
 
         if ( unlikely(__copy_field_to_guest(uop, &op, status)) )
-            return -EFAULT;
+        {
+            rc = -EFAULT;
+            break;
+        }
         guest_handle_add_offset(uop, 1);
     }
-    return 0;
+
+    gnttab_copy_release_buf(&src);
+    gnttab_copy_release_buf(&dest);
+    gnttab_copy_unlock_domains(&src, &dest);
+
+    return rc;
 }
 
 static long
--
generated by git-patchbot for /home/xen/git/xen.git#master

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