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From: Wei Liu <wei.liu2@citrix.com>
To: Samuel Thibault <samuel.thibault@ens-lyon.org>,
	Wei Liu <wei.liu2@citrix.com>,
	"Hao, Xudong" <xudong.hao@intel.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	"xen-devel@lists.xen.org" <xen-devel@lists.xen.org>,
	"stefano.stabellini@eu.citrix.com"
	<stefano.stabellini@eu.citrix.com>,
	Anthony PERARD <anthony.perard@citrix.com>
Subject: Re: pv-grub guest booting fail with recent qemu-xen
Date: Mon, 11 Apr 2016 11:54:06 +0100	[thread overview]
Message-ID: <20160411105406.GC1346@citrix.com> (raw)
In-Reply-To: <20160410201446.GN2992@var.home>

On Sun, Apr 10, 2016 at 10:14:46PM +0200, Samuel Thibault wrote:
> Hello,
> 
> > > > > +    if (prod - out_cons >= XENFB_OUT_RING_LEN) {
> > > > > +        return;
> > > > > +    }
> 
> This test seems overzealous to me: AIUI, the producer can produce
> XENFB_OUT_RING_LEN events, and thus prod - out_cons is exactly
> XENFB_OUT_RING_LEN, i.e. there is no room left at all.
> 
> The frontend part is:
> 
>    while (page->out_prod - page->out_cons == XENFB_OUT_RING_LEN)
>         schedule();
> 
> I.e. it waits while the buffer is exactly full.
> 
> So it seems to me the bug is at the backend side.
> 

OK, thanks for checking!

Hudong, can you try the following diff?

diff --git a/hw/display/xenfb.c b/hw/display/xenfb.c
index 8eb3046..284b345 100644
--- a/hw/display/xenfb.c
+++ b/hw/display/xenfb.c
@@ -789,7 +789,7 @@ static void xenfb_handle_events(struct XenFB *xenfb)

     prod = page->out_prod;
     out_cons = page->out_cons;
-    if (prod - out_cons >= XENFB_OUT_RING_LEN) {
+    if (prod - out_cons > XENFB_OUT_RING_LEN) {
         return;
     }
     xen_rmb();         /* ensure we see ring contents up to prod */

> Samuel

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  reply	other threads:[~2016-04-11 10:54 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-03-02  7:16 pv-grub guest booting fail with recent qemu-xen Hao, Xudong
2016-03-25 18:57 ` Konrad Rzeszutek Wilk
2016-03-28  2:03   ` Hao, Xudong
2016-03-28 13:21     ` Konrad Rzeszutek Wilk
2016-03-29  1:44       ` Hao, Xudong
2016-03-29 16:58       ` Wei Liu
2016-03-30  2:05         ` Hao, Xudong
2016-04-01 15:54           ` Konrad Rzeszutek Wilk
2016-04-05  1:26             ` Hao, Xudong
2016-04-05 15:41               ` Wei Liu
2016-04-10 20:14                 ` Samuel Thibault
2016-04-11 10:54                   ` Wei Liu [this message]
2016-04-11 11:52                     ` Wei Liu
2016-04-12  1:56                     ` Hao, Xudong
2016-04-12  8:28                       ` Wei Liu

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