[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] [PATCH 1/4] xen/netback: implements persistent grant with one page pool.





On 2012-11-16 17:27, Ian Campbell wrote:
On Fri, 2012-11-16 at 02:18 +0000, ANNIE LI wrote:
In this patch,
The maximum of memory overhead is about

(XEN_NETIF_TX_RING_SIZE+XEN_NETIF_RX_RING_SIZE)*PAGE_SIZE  (plus size of 
grant_ref_t and handle)
which is about 512 PAGE_SIZE. Normally, without heavy network offload, this 
maximum can not be reached.

In next patch of splitting tx/rx pool, the maximum is about
"about" or just "is"?

For only grant pages, it is this value. I took into account other element of grant_ref_t and map(change to handle in future)....


  (256+512)PAGE_SIZE.
IOW 3MB.

+
+       return NULL;
+}
+
@@ -1338,7 +1497,11 @@ static unsigned xen_netbk_tx_build_gops(struct xen_netbk 
*netbk)
                  gop->source.domid = vif->domid;
                  gop->source.offset = txreq.offset;

-               gop->dest.u.gmfn = virt_to_mfn(page_address(page));
+               if (!vif->persistent_grant)
+                       gop->dest.u.gmfn = virt_to_mfn(page_address(page));
+               else
+                       gop->dest.u.gmfn = (unsigned long)page_address(page);
page_address doesn't return any sort of frame number, does it? This is
rather confusing...
Yes. I only use dest.u.gmfn element to save the page_address here for
future memcpy, and it does not mean to use frame number actually. To
avoid confusion, here I can use

gop->dest.u.gmfn = virt_to_mfn(page_address(page));

and then call mfn_to_virt when doing memcpy.
It seems a bit odd to be using the gop structure in this way when you
aren't actually doing a grant op on it.

While investigating I noticed:
+static int
+grant_memory_copy_op(unsigned int cmd, void *vuop, unsigned int count,
+                    struct xen_netbk *netbk, bool tx_pool)
...
+       struct gnttab_copy *uop = vuop;

Why void *vuop? Why not struct gnttab_copy * in the parameter?

Sorry, my mistake.


I also noticed your new grant_memory_copy_op() seems to have unbatched
the grant ops in the non-persistent case, which is going to suck for
performance in non-persistent mode. You need to pull the conditional and
the HYPERVISOR_grant_table_op outside the loop and pass it full array
instead of doing them one at a time.

This still connects with netback per-VIF implementation.
Currently, these could not be pulled out outside since netback queue may contains persistent and nonpersistent in the same queue. I did consider to implement per-VIF first and then the persistent grant, but thinking of it is part of wei's patch combined with other patches, and finally decided to implement per-VIF later.

But this does limit implementation of persistent grant.

Thanks
Annie

Ian


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel


 


Rackspace

Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.