* Maxime Coquelin (maxime.coque...@redhat.com) wrote: > > > On 12/07/2017 05:25 PM, Dr. David Alan Gilbert wrote: > > * Maxime Coquelin (maxime.coque...@redhat.com) wrote: > > > Hi David, > > > > > > On 12/05/2017 06:41 PM, Dr. David Alan Gilbert wrote: > > > > Hi, > > > > Since I'm reworking the memory map update code I've been > > > > trying to test it with hot adding RAM; but even on upstream > > > > I'm finding that hot adding RAM causes the guest to stop passing > > > > packets with vhost-user-bridge; have either of you seen the same > > > > thing? > > > > > > No, I have never tried this. > > > > Would you know if it works on dpdk? > > We have a known issue in DPDK, the PMD threads might be accessing the > guest memory while the vhost-user protocol thread is unmapping it. > > We have a similar problem with dirty logging area, and Victor is working > on a patch that will fix both issues. > > Once ready, I'll have a try and let you know. > > > > > I'm doing: > > > > ./tests/vhost-user-bridge -u /tmp/vubrsrc.sock > > > > $QEMU -enable-kvm -m 1G,maxmem=2G,slots=4 -smp 2 -object > > > > memory-backend-file,id=mem,size=1G,mem-path=/dev/shm,share=on -numa > > > > node,memdev=mem -mem-prealloc -trace events=vhost-trace-file -chardev > > > > socket,id=char0,path=/tmp/vubrsrc.sock -netdev > > > > type=vhost-user,id=mynet1,chardev=char0,vhostforce -device > > > > virtio-net-pci,netdev=mynet1 $IMAGE -net none > > > > > > > > (with a f27 guest) and then doing: > > > > (qemu) object_add > > > > memory-backend-file,id=mem1,size=256M,mem-path=/dev/shm > > > > (qemu) device_add pc-dimm,id=dimm1,memdev=mem1 > > > > > > > > but then not getting any responses inside the guest. > > > > > > > > I can see the code sending another set-mem-table with the > > > > extra chunk of RAM and fd, and I think I can see the bridge > > > > mapping it. > > > > > > I think there are at least two problems. > > > The first one is that vhost-user-bridge does not support vhost-user > > > protocol's reply-ack feature. So when QEMU sends the requests, it cannot > > > know whether/when it has been handled by the backend. > > > > Wouldn't you have to be unlucky to cause that a problem - i.e. the > > descriptors would have to get allocated in the new RAM? > > Yes, you may be right. I think it is worth to debug it to understand > what is going on. > > > > It had been fixed by sending a GET_FEATURE requests to be sure the > > > SET_MEM_TABLE was handled, as messages are processed in order. The problem > > > is that it caused some test failures when using TCG, so it got > > > reverted. > > > > > > The initial fix: > > > > > > commit 28ed5ef16384f12500abd3647973ee21b03cbe23 > > > Author: Prerna Saxena <prerna.sax...@nutanix.com> > > > Date: Fri Aug 5 03:53:51 2016 -0700 > > > > > > vhost-user: Attempt to fix a race with set_mem_table. > > > > > > The revert: > > > > > > commit 94c9cb31c04737f86be29afefbff401cd23bc24d > > > Author: Michael S. Tsirkin <m...@redhat.com> > > > Date: Mon Aug 15 16:35:24 2016 +0300 > > > > > > Revert "vhost-user: Attempt to fix a race with set_mem_table." > > > > > > > Do we know which tests fail? > > vhost-user-test, but it should no more be failing now that it no more > uses TCG. > > I think we could consider reverting the revert. i.e. send get_features > in set_mem_table toi be sure it has been handled.
How does it fail? Does it fail every time or only some times? (The postcopy test in migration-test.c also fails under TCG under very heavy load and I've not figured out why yet). Dave > > > Another problem is that memory mmapped with previous call does not seems > > > to be unmapped, but that should not cause other problems than leaking > > > virtual memory. > > > > Oh, leaks are the least of our problem there! > > Sure. > > Maxime > > Dave > > > > > Maxime > > > > Dave > > > > > > > > -- > > > > Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK > > > > > > -- > > Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK > > -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
