Re: [PATCH 2/2] vhost: lockless enqueuing

On 04/26/2016 02:24 PM, Pankaj Gupta wrote:

Hi Jason,

Overall patches look good. Just one doubt I have is below:

quoted

We use spinlock to synchronize the work list now which may cause
unnecessary contentions. So this patch switch to use llist to remove
this contention. Pktgen tests shows about 5% improvement:

Before:
~1300000 pps
After:
~1370000 pps

Signed-off-by: Jason Wang <redacted>
---
 drivers/vhost/vhost.c | 52
 +++++++++++++++++++++++++--------------------------
 drivers/vhost/vhost.h |  7 ++++---
 2 files changed, 29 insertions(+), 30 deletions(-)

[...]

quoted

-		if (work) {
+		node = llist_del_all(&dev->work_list);
+		if (!node)
+			schedule();
+
+		node = llist_reverse_order(node);

Can we avoid llist reverse here?

Probably not, this is because:

- we should process the work exactly the same order as they were queued,
otherwise flush won't work
- llist can only add a node to the head of list.

Thanks