linux-kernel - Re: [Patch v2] uio_hv_generic: Set event for all channels on the device

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Message-ID: <20250309054727.GA24737@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net>
Date: Sat, 8 Mar 2025 21:47:27 -0800
From: Saurabh Singh Sengar <ssengar@...ux.microsoft.com>
To: longli@...uxonhyperv.com
Cc: "K. Y. Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
	Long Li <longli@...rosoft.com>
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, longli@...uxonhyperv.com wrote:
> From: Long Li <longli@...rosoft.com>
> 
> 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 <longli@...rosoft.com>
> ---
> 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