Re: [Qemu-devel] [PATCH v2 1/2] net: introduce MAC_TABLE_CHANGED event

[Michael S. Tsirkin]

On Tue, Jun 04, 2013 at 03:42:19PM +0800, Amos Kong wrote:
> On Tue, Jun 04, 2013 at 02:43:11PM +0800, Amos Kong wrote:
> > 
> 
> 
> > I did more tests in clear environment, and found that the guest hang/slow
> > (no response from monitor) is caused by flooding events. I could not
> > reproduce it with upstream qemu [1]
> > 
> > If I set event_throttle to 1 ~ 1000, the problem doesn't occur.
> > 
> > It's easier to reproduce this problem by changing vlan config,
> > not because it passes more data with VQ cmd, but it will cause more
> > events.
> > 
> > 
> > In this case, we can set event_throttle to 1 for _RX_FILTER_CHANGED
> > event to avoid it slows guest. The 1 ms delay should be acceptabled?
> 
> Just discussed with mst in IRC.
> 
> Here we have two problem:
> (1) huge number of events will flood monitor client (management),
> (2) emitting huge number of events will slow guest itself.
> 
> Both the flag (nc->rxfilter_notify_enabled) and event_throttle API
> can be used to avoid problem (1).
> 
> Event_throttle API can clearly avoid problem (2).
> 
> In real testing, I found it's difficult to reproduce problem (2) if we
> already use the flag. It seems response time is larger enough, some
> events will be dropped, guest could not be slowed.
> 
> Michael told me that we have many ways to slow guest itself, so it's
> not a big issue here.
> 
> We care about the delay of responsing event, so we should only use
> control flag (As my patch v4).
> 
> What's your opinion?

Sounds reasonable.
Pls send v3 and we'll discuss :)