linux-kernel - RE: [RFC PATCH 6/6] Drivers: hv: vmbus: Refactor the ring-buffer iterator functions

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Date:   Fri, 15 Apr 2022 16:44:50 +0000
From:   "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
To:     Andrea Parri <parri.andrea@...il.com>
CC:     KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
        Stefano Garzarella <sgarzare@...hat.com>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [RFC PATCH 6/6] Drivers: hv: vmbus: Refactor the ring-buffer
 iterator functions

From: Andrea Parri <parri.andrea@...il.com> Sent: Friday, April 15, 2022 9:28 AM
> 
> On Fri, Apr 15, 2022 at 09:00:31AM +0200, Andrea Parri wrote:
> > > > @@ -470,7 +471,6 @@ struct vmpacket_descriptor *hv_pkt_iter_first_raw(struct
> > > > vmbus_channel *channel)
> > > >
> > > >  	return (struct vmpacket_descriptor *)(hv_get_ring_buffer(rbi) + rbi-
> > > > >priv_read_index);
> > > >  }
> > > > -EXPORT_SYMBOL_GPL(hv_pkt_iter_first_raw);
> > >
> > > Does hv_pkt_iter_first_raw() need to be retained at all as a
> > > separate function?  I think after these changes, the only caller
> > > is hv_pkt_iter_first(), in which case the code could just go
> > > inline in hv_pkt_iter_first().  Doing that combining would
> > > also allow the elimination of the duplicate call to
> > > hv_pkt_iter_avail().
> 
> Back to this, can you clarify what you mean by "the elimination of..."?
> After moving the function "inline", hv_pkt_iter_avail() would be called
> in to check for a non-NULL descriptor (in the inline function) and later
> in the computation of bytes_avail.

I was thinking something like this:

bytes_avail = hv_pkt_iter_avail(rbi);
if (bytes_avail < sizeof(struct vmpacket_descriptor))
	return NULL;
bytes_avail = min(rbi->pkt_buffer_size, bytes_avail);

desc = (struct vmpacket_descriptor *)(hv_get_ring_buffer(rbi) + rbi->priv_read_index);

And for that matter, hv_pkt_iter_avail() is now only called in one place.
It's a judgment call whether to keep it as a separate helper function vs.
inlining it in hv_pkt_iter_first() as well.  I'm OK either way.


Michael