On 08/13/2009 09:33 AM, Shirley Ma wrote:
Guest virtio_net receives packets from its pre-allocated vring
buffers, then it delivers these packets to upper layer protocols
as skb buffs. So it's not necessary to pre-allocate skb for each
mergable buffer, then frees it when it's useless.
This patch has deferred skb allocation to when receiving packets,
it reduces skb pre-allocations and skb_frees. And it induces two
page list: freed_pages and used_page list, used_pages is used to
track pages pre-allocated, it is only useful when removing virtio_net.
This patch has tested and measured against 2.6.31-rc4 git,
I thought this patch will improve large packet performance, but I saw
netperf TCP_STREAM performance improved for small packet for both
local guest to host and host to local guest cases. It also reduces
UDP packets drop rate from host to local guest. I am not fully understand
why.
The netperf results from my laptop are:
mtu=1500
netperf -H xxx -l 120
w/o patch w/i patch (two runs)
guest to host: 3336.84Mb/s 3730.14Mb/s ~ 3582.88Mb/s
host to guest: 3165.10Mb/s 3370.39Mb/s ~ 3407.96Mb/s
Here is the patch for your review. The same approach can apply to non-mergable
buffs too, so we can use code in common. If there is no objection, I will
submit the non-mergable buffs patch later.
Signed-off-by: Shirley Ma<xma@xxxxxxxxxx>
---
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 2a6e81d..e31ebc9 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -17,6 +17,7 @@
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
//#define DEBUG
+#include<linux/list.h>
#include<linux/netdevice.h>
#include<linux/etherdevice.h>
#include<linux/ethtool.h>
@@ -39,6 +40,12 @@ module_param(gso, bool, 0444);
#define VIRTNET_SEND_COMMAND_SG_MAX 2
+struct page_list
+{
+ struct page *page;
+ struct list_head list;
+};
This is an inefficient way to store a list of pages. Each page requires
an allocation and a cache line.
Alternatives include:
- store the link in the page itself
- have an array of pages per list element instead of just one pointer
- combine the two, store an array of page pointers in one of the free pages
- use the struct page::lru member
The last is the most traditional and easiest so I'd recommend it (though
it still takes the cacheline hit).
+static struct page_list *get_a_free_page(struct virtnet_info *vi, gfp_t gfp_mask)
+{
+ struct page_list *plist;
+
+ if (list_empty(&vi->freed_pages)) {
+ plist = kmalloc(sizeof(struct page_list), gfp_mask);
+ if (!plist)
+ return NULL;
+ list_add_tail(&plist->list,&vi->freed_pages);
+ plist->page = alloc_page(gfp_mask);
What if the allocation fails here?
--
error compiling committee.c: too many arguments to function
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