similar to: [PATCH RFC] vhost: fix barrier pairing

With PUBLISH_USED_IDX, guest tells us which used entries it has consumed. This can be used to reduce the number of interrupts: after we write a used entry, if the guest has not yet consumed the previous entry, or if the guest has already consumed the new entry, we do not need to interrupt. This imporves bandwidth by 30% under some workflows. Signed-off-by: Michael S. Tsirkin <mst at

With PUBLISH_USED_IDX, guest tells us which used entries it has consumed. This can be used to reduce the number of interrupts: after we write a used entry, if the guest has not yet consumed the previous entry, or if the guest has already consumed the new entry, we do not need to interrupt. This imporves bandwidth by 30% under some workflows. Signed-off-by: Michael S. Tsirkin <mst at

With PUBLISH_USED_IDX, guest tells us which used entries it has consumed. This can be used to reduce the number of interrupts: after we write a used entry, if the guest has not yet consumed the previous entry, or if the guest has already consumed the new entry, we do not need to interrupt. This imporves bandwidth by 30% under some workflows. Signed-off-by: Michael S. Tsirkin <mst at

With PUBLISH_USED_IDX, guest tells us which used entries it has consumed. This can be used to reduce the number of interrupts: after we write a used entry, if the guest has not yet consumed the previous entry, or if the guest has already consumed the new entry, we do not need to interrupt. This imporves bandwidth by 30% under some workflows. Signed-off-by: Michael S. Tsirkin <mst at

Documentation/memory-barriers.txt says: Mandatory barriers should not be used to control SMP effects, since mandatory barriers unnecessarily impose overhead on UP systems. This rule applies to virtio, so let's do it correctly. Signed-off-by: Michael S. Tsirkin <mst at redhat.com> --- drivers/virtio/virtio_ring.c | 12 ++++++------ 1 files changed, 6 insertions(+), 6 deletions(-)

Documentation/memory-barriers.txt says: Mandatory barriers should not be used to control SMP effects, since mandatory barriers unnecessarily impose overhead on UP systems. This rule applies to virtio, so let's do it correctly. Signed-off-by: Michael S. Tsirkin <mst at redhat.com> --- drivers/virtio/virtio_ring.c | 12 ++++++------ 1 files changed, 6 insertions(+), 6 deletions(-)

We currently fill all of RX ring, then add_buf returns ENOSPC, which gets mis-detected as an out of memory condition and causes us to reschedule the work, and so on forever. Fix this by oom = err == -ENOMEM; Signed-off-by: Michael S. Tsirkin <mst at redhat.com> --- Rusty, please review the following patch for 2.6.35. drivers/net/virtio_net.c | 7 +++---- 1 files changed, 3

We currently fill all of RX ring, then add_buf returns ENOSPC, which gets mis-detected as an out of memory condition and causes us to reschedule the work, and so on forever. Fix this by oom = err == -ENOMEM; Signed-off-by: Michael S. Tsirkin <mst at redhat.com> --- Rusty, please review the following patch for 2.6.35. drivers/net/virtio_net.c | 7 +++---- 1 files changed, 3

virtio net will never try to overflow the TX ring, so the only reason add_buf may fail is out of memory. Thus, we can not stop the device until some request completes - there's no guarantee anything at all is outstanding. Make the error message clearer as well: error here does not indicate queue full. Signed-off-by: Michael S. Tsirkin <mst at redhat.com> --- drivers/net/virtio_net.c |

virtio net will never try to overflow the TX ring, so the only reason add_buf may fail is out of memory. Thus, we can not stop the device until some request completes - there's no guarantee anything at all is outstanding. Make the error message clearer as well: error here does not indicate queue full. Signed-off-by: Michael S. Tsirkin <mst at redhat.com> --- drivers/net/virtio_net.c |

Userspace virtio server has the following hack so guests rely on it, and we have to replicate it, too: use source port to detect incoming IPv4 DHCP response packets, and fill in the checksum for these. The issue we are solving is that on linux guests, some apps that use recvmsg with AF_PACKET sockets, don't know how to handle CHECKSUM_PARTIAL; The interface to return the relevant information

Userspace virtio server has the following hack so guests rely on it, and we have to replicate it, too: use source port to detect incoming IPv4 DHCP response packets, and fill in the checksum for these. The issue we are solving is that on linux guests, some apps that use recvmsg with AF_PACKET sockets, don't know how to handle CHECKSUM_PARTIAL; The interface to return the relevant information

virtio-pci resets the device at startup by writing to the status register, but this does not clear the pci config space, specifically msi enable status which affects register layout. This breaks things like kdump when they try to use e.g. virtio-blk. Fix by forcing msi off at startup. Since pci.c already has a routine to do this, we export and use it instead of duplicating code. Signed-off-by:

virtio-pci resets the device at startup by writing to the status register, but this does not clear the pci config space, specifically msi enable status which affects register layout. This breaks things like kdump when they try to use e.g. virtio-blk. Fix by forcing msi off at startup. Since pci.c already has a routine to do this, we export and use it instead of duplicating code. Signed-off-by:

virtio is communicating with a virtual "device" that actually runs on another host processor. Thus SMP barriers can be used to control memory access ordering. Where possible, we should use SMP barriers which are more lightweight than mandatory barriers, because mandatory barriers also control MMIO effects on accesses through relaxed memory I/O windows (which virtio does not use)

virtio is communicating with a virtual "device" that actually runs on another host processor. Thus SMP barriers can be used to control memory access ordering. Where possible, we should use SMP barriers which are more lightweight than mandatory barriers, because mandatory barriers also control MMIO effects on accesses through relaxed memory I/O windows (which virtio does not use)

Hello Rusty, seems that we still have a problem with virtio_net and the enable_cb callback. During a long running network stress tests with virtio and got the following oops: ------------[ cut here ]------------ kernel BUG at drivers/virtio/virtio_ring.c:230! illegal operation: 0001 [#1] SMP Modules linked in: CPU: 0 Not tainted 2.6.26-rc2-kvm-00436-gc94c08b-dirty #34 Process netserver (pid:

Hello Rusty, seems that we still have a problem with virtio_net and the enable_cb callback. During a long running network stress tests with virtio and got the following oops: ------------[ cut here ]------------ kernel BUG at drivers/virtio/virtio_ring.c:230! illegal operation: 0001 [#1] SMP Modules linked in: CPU: 0 Not tainted 2.6.26-rc2-kvm-00436-gc94c08b-dirty #34 Process netserver (pid:

Hello everyone, everytime I run on a puppet host: #puppet agent --test I see this commet: info: Applying configuration version ''000001'' then lets say I deploy a new package from my local repository, from which I would get a different configuration version. #puppet agent --test info: Applying configuration version ''000002'' ...question: is there a way to

Hi Dave, Nice driver optimization from Shirley, but requires a new virtio hook. Do you want to take both? I have nothing else overlapping it. Cheers, Rusty.