linux-kernel - Re: [Xen-devel] [PATCH v2 09/13] xen/pvcalls: implement recvmsg

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Date:   Wed, 26 Jul 2017 17:08:36 -0700 (PDT)
From:   Stefano Stabellini <sstabellini@...nel.org>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>
cc:     Stefano Stabellini <sstabellini@...nel.org>,
        xen-devel@...ts.xen.org, jgross@...e.com,
        Stefano Stabellini <stefano@...reto.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [Xen-devel] [PATCH v2 09/13] xen/pvcalls: implement recvmsg

On Wed, 26 Jul 2017, Boris Ostrovsky wrote:
> >> +			count++;
> >> +		else
> >> +			wait_event_interruptible(map->active.inflight_conn_req,
> >> +						 pvcalls_front_read_todo(map));
> >> +	}
> > Should we be using PVCALLS_FRONT_MAX_SPIN here? In sendmsg it is
> > counting non-sleeping iterations but here we are sleeping so
> > PVCALLS_FRONT_MAX_SPIN (5000) may take a while.
> >
> > In fact, what shouldn't this waiting be a function of MSG_DONTWAIT
> 
> err, which it already is. But the question still stands (except for
> MSG_DONTWAIT).

The code (admittedly unintuitive) is busy-looping (non-sleeping) for
5000 iterations *before* attempting to sleep. So in that regard, recvmsg
and sendmsg use PVCALLS_FRONT_MAX_SPIN in the same way: only for
non-sleeping iterations.