Stefano Stabellini
2012-Mar-27 17:03 UTC
[PATCH v2 1/2] xen: enter/exit lazy_mmu_mode around m2p_override calls
This patch is a significant performance improvement for the
m2p_override: about 6% using the gntdev device.
Each m2p_add/remove_override call issues a MULTI_grant_table_op and a
__flush_tlb_single if kmap_op != NULL. Batching all the calls together
is a great performance benefit because it means issuing one hypercall
total rather than two hypercall per page.
If paravirt_lazy_mode is set PARAVIRT_LAZY_MMU, all these calls are
going to be batched together, otherwise they are issued one at a time.
Adding arch_enter_lazy_mmu_mode/arch_leave_lazy_mmu_mode around the
m2p_add/remove_override calls forces paravirt_lazy_mode to
PARAVIRT_LAZY_MMU, therefore makes sure that they are always batched.
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
---
drivers/block/xen-blkback/blkback.c | 4 ++++
drivers/xen/grant-table.c | 8 ++++++++
2 files changed, 12 insertions(+), 0 deletions(-)
diff --git a/drivers/block/xen-blkback/blkback.c
b/drivers/block/xen-blkback/blkback.c
index 0088bf6..60abff6 100644
--- a/drivers/block/xen-blkback/blkback.c
+++ b/drivers/block/xen-blkback/blkback.c
@@ -342,6 +342,7 @@ static void xen_blkbk_unmap(struct pending_req *req)
* Note, we use invcount, so nr->pages, so we can''t index
* using vaddr(req, i).
*/
+ arch_enter_lazy_mmu_mode();
for (i = 0; i < invcount; i++) {
ret = m2p_remove_override(
virt_to_page(unmap[i].host_addr), false);
@@ -351,6 +352,7 @@ static void xen_blkbk_unmap(struct pending_req *req)
continue;
}
}
+ arch_leave_lazy_mmu_mode();
}
static int xen_blkbk_map(struct blkif_request *req,
@@ -386,6 +388,7 @@ static int xen_blkbk_map(struct blkif_request *req,
* so that when we access vaddr(pending_req,i) it has the contents of
* the page from the other domain.
*/
+ arch_enter_lazy_mmu_mode();
for (i = 0; i < nseg; i++) {
if (unlikely(map[i].status != 0)) {
pr_debug(DRV_PFX "invalid buffer -- could not remap it\n");
@@ -410,6 +413,7 @@ static int xen_blkbk_map(struct blkif_request *req,
seg[i].buf = map[i].dev_bus_addr |
(req->u.rw.seg[i].first_sect << 9);
}
+ arch_leave_lazy_mmu_mode();
return ret;
}
diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
index b4d4eac..c7dc2d6 100644
--- a/drivers/xen/grant-table.c
+++ b/drivers/xen/grant-table.c
@@ -751,6 +751,8 @@ int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
if (xen_feature(XENFEAT_auto_translated_physmap))
return ret;
+ arch_enter_lazy_mmu_mode();
+
for (i = 0; i < count; i++) {
/* Do not add to override if the map failed. */
if (map_ops[i].status)
@@ -769,6 +771,8 @@ int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
return ret;
}
+ arch_leave_lazy_mmu_mode();
+
return ret;
}
EXPORT_SYMBOL_GPL(gnttab_map_refs);
@@ -785,12 +789,16 @@ int gnttab_unmap_refs(struct gnttab_unmap_grant_ref
*unmap_ops,
if (xen_feature(XENFEAT_auto_translated_physmap))
return ret;
+ arch_enter_lazy_mmu_mode();
+
for (i = 0; i < count; i++) {
ret = m2p_remove_override(pages[i], clear_pte);
if (ret)
return ret;
}
+ arch_leave_lazy_mmu_mode();
+
return ret;
}
EXPORT_SYMBOL_GPL(gnttab_unmap_refs);
--
1.7.2.5