> Subject: Re: [Patch v2] uio_hv_generic: Set event for all channels on the > device > > On Fri, Feb 28, 2025 at 02:14:14PM -0800, [email protected] wrote: > > From: Long Li <[email protected]> > > > > Hyper-V may offer a non latency sensitive device with subchannels > > without monitor bit enabled. The decision is entirely on the Hyper-V > > host not configurable within guest. > > > > When a device has subchannels, also signal events for the subchannel > > if its monitor bit is disabled. > > > > Signed-off-by: Long Li <[email protected]> > > --- > > Change log > > v2: Use vmbus_set_event() to avoid additional check on monitored bit > > Lock vmbus_connection.channel_mutex when going through subchannels > > > > drivers/uio/uio_hv_generic.c | 32 ++++++++++++++++++++++++++------ > > 1 file changed, 26 insertions(+), 6 deletions(-) > > > > diff --git a/drivers/uio/uio_hv_generic.c > > b/drivers/uio/uio_hv_generic.c index 3976360d0096..45be2f8baade 100644 > > --- a/drivers/uio/uio_hv_generic.c > > +++ b/drivers/uio/uio_hv_generic.c > > @@ -65,6 +65,16 @@ struct hv_uio_private_data { > > char send_name[32]; > > }; > > > > +static void set_event(struct vmbus_channel *channel, s32 irq_state) { > > + channel->inbound.ring_buffer->interrupt_mask = !irq_state; > > + if (!channel->offermsg.monitor_allocated && irq_state) { > > + /* MB is needed for host to see the interrupt mask first */ > > + virt_mb(); > > Why is memory barrier not getting called for 'faster' channels ? > > - Saurabh
No, the memory barrier is not needed. Even with a barrier, There is no guarantee that all pending IRQs are flushed when hv_uio_irqcontrol() returns. If user-mode depends on this guarantee, that user-mode has a bug. This barrier adds unnecessary costs when walking through subchannels. Long
