[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
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