Re: [Qemu-devel] [PATCH v5 04/12] block/io_uring: implements interfaces for io_uring

From: Stefan Hajnoczi <stefanha@redhat.com>
To: Fam Zheng <fam@euphon.net>
Cc: Kevin Wolf <kwolf@redhat.com>, Sergio Lopez <slp@redhat.com>,
	qemu-block@nongnu.org, qemu-devel@nongnu.org,
	Max Reitz <mreitz@redhat.com>,
	saket.sinha89@gmail.com, Paolo Bonzini <pbonzini@redhat.com>,
	Maxim Levitsky <mlevitsk@redhat.com>,
	Julia Suvorova <jusual@mail.ru>,
	Aarushi Mehta <mehta.aaru20@gmail.com>,
	Markus Armbruster <armbru@redhat.com>
Subject: Re: [Qemu-devel] [PATCH v5 04/12] block/io_uring: implements interfaces for io_uring
Date: Wed, 12 Jun 2019 15:43:40 +0100	[thread overview]
Message-ID: <20190612144340.GF19156@stefanha-x1.localdomain> (raw)
In-Reply-To: <20190611111714.wshlk6fddh34atfp@debian>

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On Tue, Jun 11, 2019 at 07:17:14PM +0800, Fam Zheng wrote:
> On Mon, 06/10 19:18, Aarushi Mehta wrote:
> > +        /* Prevent infinite loop if submission is refused */
> > +        if (ret <= 0) {
> > +            if (ret == -EAGAIN) {
> > +                continue;
> > +            }
> > +            break;
> > +        }
> > +        s->io_q.in_flight += ret;
> > +        s->io_q.in_queue  -= ret;
> > +    }
> > +    s->io_q.blocked = (s->io_q.in_queue > 0);
> 
> I'm confused about s->io_q.blocked. ioq_submit is where it gets updated, but
> if it becomes true, calling ioq_submit will be fenced. So how does it get
> cleared?

When blocked, additional I/O requests are not submitted until the next
completion.  See qemu_luring_process_completions_and_submit() for the
code path where ioq_submit() gets called again.

Stefan

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