On Mon, Aug 05, 2019 at 12:41:45PM +0800, Jason Wang wrote:
On 2019/8/5 äå12:36, Jason Wang wrote:As is, with preempt enabled? Nope I don't think blocking an invalidator
On 2019/8/2 äå10:27, Michael S. Tsirkin wrote:
On Fri, Aug 02, 2019 at 09:46:13AM -0300, Jason Gunthorpe wrote:
On Fri, Aug 02, 2019 at 05:40:07PM +0800, Jason Wang wrote:The topic is whether we should revert
I've also idly wondered if calling synchronize_rcu() under the variousThis must be a proper barrier, like a spinlock, mutex, orI start with synchronize_rcu() but both you and Michael raise some
synchronize_rcu.
concern.
mm locks is a deadlock situation.
Then I try spinlock and mutex:I think the topic here is correctness not performance improvement
1) spinlock: add lots of overhead on datapath, this leads 0
performance
improvement.
commit 7f466032dc9 ("vhost: access vq metadata through kernel
virtual address")
or keep it in. The only reason to keep it is performance.
Maybe it's time to introduce the config option?
Or does it make sense if I post a V3 with:
- introduce config option and disable the optimization by default
- switch from synchronize_rcu() to vhost_flush_work(), but the rest are the
same
This can give us some breath to decide which way should go for next release?
Thanks
on swap IO is ok, so I don't believe this stuff is going into this
release at this point.
So it's more a question of whether it's better to revert and apply a clean
patch on top, or just keep the code around but disabled with an ifdef as is.
I'm open to both options, and would like your opinion on this.
Now as long as all this code is disabled anyway, we can experiment a
bit.
I personally feel we would be best served by having two code paths:
- Access to VM memory directly mapped into kernel
- Access to userspace
Having it all cleanly split will allow a bunch of optimizations, for
example for years now we planned to be able to process an incoming short
packet directly on softirq path, or an outgoing on directly within
eventfd.
It's not hard consider we've already had our own accssors. But the
question is (as asked in another thread), do you want permanent GUP or
still use MMU notifiers.
Thanks
_______________________________________________
Virtualization mailing list
Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
https://lists.linuxfoundation.org/mailman/listinfo/virtualization