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Re: [Qemu-devel] [Qemu-block] [PATCH v3 03/13] l2tpv3: Drop l2tpv3_can_s

From: Fam Zheng
Subject: Re: [Qemu-devel] [Qemu-block] [PATCH v3 03/13] l2tpv3: Drop l2tpv3_can_send
Date: Tue, 26 May 2015 14:52:48 +0800
User-agent: Mutt/1.5.23 (2014-03-12)

On Tue, 05/19 15:48, Stefan Hajnoczi wrote:
> On Tue, May 19, 2015 at 10:51:00AM +0000, Fam Zheng wrote:
> > This callback is called by main loop before polling s->fd, if it returns
> > false, the fd will not be polled in this iteration.
> > 
> > This is redundant with checks inside read callback. After this patch,
> > the data will be copied from s->fd to s->msgvec when it arrives. If the
> > device can't receive, it will be queued to incoming_queue, and when the
> > device status changes, this queue will be flushed.
> This doesn't work because s->msgvec can fill up when
> qemu_can_send_packet() returns false.  At that point we burn 100% CPU
> because the file descriptor is still being monitored.

If qemu_can_send_packet returns false, we do stop monitoring the fd. In

    size = qemu_send_packet_async(
    if (size == 0) {
        l2tpv3_read_poll(s, false);

The packet is queued and size is 0, so the read poll will be disabled until
it's flushed.

What am I missing?


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