virtio-s390 on kvm can use a cookie value passed to guest to optimize channel/VQ lookups. Document this. Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx> --- diff --git a/virtio-spec.lyx b/virtio-spec.lyx index 72d956c..91aed06 100644 --- a/virtio-spec.lyx +++ b/virtio-spec.lyx @@ -10627,7 +10626,252 @@ Guest->Host Notification For notifying the host of virtqueue buffers, the guest unfortunately can't use a channel command (the asynchronous characteristics of channel I/O interact badly with the host block I/O backend). - Instead, it uses a diagnose 0x500 call with subcode 3 specifying the queue. + Instead, it uses a diagnose 0x500 call with subcode 3 specifying the queue +\change_inserted 1986246365 1362677938 +, as follows: +\end_layout + +\begin_layout Standard + +\change_inserted 1986246365 1362677973 +\begin_inset Tabular +<lyxtabular version="3" rows="5" columns="3"> +<features tabularvalignment="middle"> +<column alignment="center" valignment="top" width="0"> +<column alignment="center" valignment="top" width="0"> +<column alignment="center" valignment="top" width="0"> +<row> +<cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> +\begin_inset Text + +\begin_layout Plain Layout + +\change_inserted 1986246365 1362677978 +GPR +\change_unchanged + +\end_layout + +\end_inset +</cell> +<cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> +\begin_inset Text + +\begin_layout Plain Layout + +\change_inserted 1986246365 1362678629 +Input Value +\change_unchanged + +\end_layout + +\end_inset +</cell> +<cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" rightline="true" usebox="none"> +\begin_inset Text + +\begin_layout Plain Layout + +\change_inserted 1986246365 1362678627 +Output Value +\end_layout + +\end_inset +</cell> +</row> +<row> +<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> +\begin_inset Text + +\begin_layout Plain Layout + +\change_inserted 1986246365 1362677991 +1 +\change_unchanged + +\end_layout + +\end_inset +</cell> +<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> +\begin_inset Text + +\begin_layout Plain Layout + +\change_inserted 1986246365 1362678208 +0x3 +\change_unchanged + +\end_layout + +\end_inset +</cell> +<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> +\begin_inset Text + +\begin_layout Plain Layout + +\change_inserted 1986246365 1362678620 + +\end_layout + +\end_inset +</cell> +</row> +<row> +<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> +\begin_inset Text + +\begin_layout Plain Layout + +\change_inserted 1986246365 1362678226 +2 +\change_unchanged + +\end_layout + +\end_inset +</cell> +<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> +\begin_inset Text + +\begin_layout Plain Layout + +\change_inserted 1986246365 1362678498 +Subchannel ID +\change_unchanged + +\end_layout + +\end_inset +</cell> +<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> +\begin_inset Text + +\begin_layout Plain Layout + +\change_inserted 1986246365 1362678642 +Host Cookie +\end_layout + +\end_inset +</cell> +</row> +<row> +<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> +\begin_inset Text + +\begin_layout Plain Layout + +\change_inserted 1986246365 1362678500 +3 +\change_unchanged + +\end_layout + +\end_inset +</cell> +<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> +\begin_inset Text + +\begin_layout Plain Layout + +\change_inserted 1986246365 1362678540 +Virtqueue number +\change_unchanged + +\end_layout + +\end_inset +</cell> +<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> +\begin_inset Text + +\begin_layout Plain Layout + +\change_inserted 1986246365 1362678620 + +\end_layout + +\end_inset +</cell> +</row> +<row> +<cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> +\begin_inset Text + +\begin_layout Plain Layout + +\change_inserted 1986246365 1362678529 +4 +\change_unchanged + +\end_layout + +\end_inset +</cell> +<cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> +\begin_inset Text + +\begin_layout Plain Layout + +\change_inserted 1986246365 1362678644 +Host Cookie +\change_unchanged + +\end_layout + +\end_inset +</cell> +<cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" rightline="true" usebox="none"> +\begin_inset Text + +\begin_layout Plain Layout + +\change_inserted 1986246365 1362678620 + +\end_layout + +\end_inset +</cell> +</row> +</lyxtabular> + +\end_inset + + +\change_deleted 1986246365 1362677938 +. +\change_inserted 1986246365 1362678646 + +\end_layout + +\begin_layout Standard + +\change_inserted 1986246365 1362679010 +Host cookie is an optional per-virtqueue 64 bit value that can be used by + the hypervisor to speed up the notification execution. + For each notification, the output value is returned in GPR2 and should + be passed in GPR4 for the next notification: +\end_layout + +\begin_layout LyX-Code + +\change_inserted 1986246365 1362679011 +\begin_inset listings +inline false +status open + +\begin_layout Plain Layout + +\change_inserted 1986246365 1362679033 + +info->cookie = do_notify(schid, virtqueue_get_queue_index(vq), info->cookie); +\end_layout + +\end_inset + + \end_layout \begin_layout Subsubsection* -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
