netdev - Re: [PATCH net-next RFC 1/3] virtio: support for urgent descriptors

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Message-ID: <5440A7DE.5030806@redhat.com>
Date:	Fri, 17 Oct 2014 13:23:42 +0800
From:	Jason Wang <jasowang@...hat.com>
To:	Rusty Russell <rusty@...tcorp.com.au>, mst@...hat.com,
	virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
CC:	linux-api@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH net-next RFC 1/3] virtio: support for urgent descriptors

On 10/15/2014 01:40 PM, Rusty Russell wrote:
> Jason Wang <jasowang@...hat.com> writes:
>> Below should be useful for some experiments Jason is doing.
>> I thought I'd send it out for early review/feedback.
>>
>> event idx feature allows us to defer interrupts until
>> a specific # of descriptors were used.
>> Sometimes it might be useful to get an interrupt after
>> a specific descriptor, regardless.
>> This adds a descriptor flag for this, and an API
>> to create an urgent output descriptor.
>> This is still an RFC:
>> we'll need a feature bit for drivers to detect this,
>> but we've run out of feature bits for virtio 0.X.
>> For experimentation purposes, drivers can assume
>> this is set, or add a driver-specific feature bit.
>>
>> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
>> Signed-off-by: Jason Wang <jasowang@...hat.com>
> The new VRING_DESC_F_URGENT bit is theoretically nicer, but for
> networking (which tends to take packets in order) couldn't we just set
> the event counter to give us a tx interrupt at the packet we want?
>
> Cheers,
> Rusty.

Yes, we could. Recent RFC of enabling tx interrupt use this.
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