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References: <20161124151225.GA11963@stefanha-x1.localdomain>
From: Eliezer Tamir <eliezer.tamir@linux.intel.com>
Message-ID: <325f739a-05bd-c437-b9a2-e371a8cbf50d@linux.intel.com>
Date: Mon, 28 Nov 2016 11:31:43 +0200
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Subject: Re: [Qemu-devel] Linux kernel polling for QEMU
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To: Stefan Hajnoczi <stefanha@redhat.com>, qemu-devel@nongnu.org
Cc: Jens Axboe <axboe@fb.com>, Christoph Hellwig <hch@lst.de>, Davide Libenzi <davidel@xmailserver.org>, "Michael S. Tsirkin" <mst@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, Christian Borntraeger <borntraeger@de.ibm.com>, Fam Zheng <famz@redhat.com>, Eric Dumazet <eric.dumazet@gmail.com>, Willem de Bruijn <willemb@google.com>

+ Eric, Willem

On 24/11/2016 17:12, Stefan Hajnoczi wrote:
> I looked through the socket SO_BUSY_POLL and blk_mq poll support in
> recent Linux kernels with an eye towards integrating the ongoing QEMU
> polling work.  The main missing feature is eventfd polling support which
> I describe below.
...
> State of polling in Linux
> -------------------------
> SO_BUSY_POLL causes recvmsg(2), select(2), and poll(2) family system
> calls to spin awaiting new receive packets.  From what I can tell epoll
> is not supported so that system call will sleep without polling.

At the time I sent out an RFC for epoll() SO_BUSY_POLL support.
https://lkml.org/lkml/2013/8/21/192

In hindsight I think the way I tracked sockets was over-complicated.
What I would do today would be to extend the API to allow the user
to tell epoll which socket/queue combinations are interesting.

I would love to collaborate on this with you, though I must confess that
my resources at the moment are limited and the setup I used for testing
no longer exists.

-Eliezer