linux-kernel - Re: [PATCH] rpmsg: compute number of buffers to allocate from vrings

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Date:	Wed, 13 Aug 2014 10:47:46 -0500
From:	Suman Anna <s-anna@...com>
To:	Ohad Ben-Cohen <ohad@...ery.com>
CC:	Rusty Russell <rusty@...tcorp.com.au>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>
Subject: Re: [PATCH] rpmsg: compute number of buffers to allocate from vrings

Hi Ohad,

On 08/13/2014 08:40 AM, Ohad Ben-Cohen wrote:
> Hi Suman,
> 
> On Tue, Aug 12, 2014 at 7:19 PM, Suman Anna <s-anna@...com> wrote:
>> Yes, I was playing around with using less buffers in the remoteproc
>> resource table for the vrings. The remoteproc virtio code creates the
>> vrings using the number of buffers based on .num field value of struct
>> fw_rsc_vdev_vring in the resource table. The virtio rpmsg probe code
>> though tries to set up the receive buffers for the same virtqueue based
>> on the current hard-coded value of 512 buffers and virtqueue_add_inbuf
>> would fail as the virtqueue is created with less number of buffers and
>> throws a WARN_ON.
> 
> Gotcha - thanks for the details.
> 
> Limiting the number of buffers in case the vrings are too small makes
> sense, but let's use RPMSG_NUM_BUFS as an upper bound, so wacky
> resource tables won't trigger unreasonable memory waste.
> 
> Something in the lines of:
> 
> vrp->num_bufs = min(PMSG_NUM_BUFS, virtqueue_get_vring_size(vrp->rvq) * 2);
> 
> Should probably do the trick.
> 
> Does this satisfy your requirement?

Yeah, this will work for me. I will go ahead and add a WARN_ON as well
to detect above wacky condition, and if someone really needs more
buffers in the future, we can revisit this.

regards
Suman
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