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Date: Mon, 19 Feb 2024 11:02:54 +0100
From: Greg KH <gregkh@linuxfoundation.org>
To: Saurabh Singh Sengar <ssengar@linux.microsoft.com>
Cc: kys@microsoft.com, haiyangz@microsoft.com, wei.liu@kernel.org,
	decui@microsoft.com, linux-hyperv@vger.kernel.org,
	linux-kernel@vger.kernel.org, ssengar@microsoft.com
Subject: Re: [PATCH 2/6] uio_hv_generic: Query the ringbuffer size for device
Message-ID: <2024021931-heroics-ducktail-e7aa@gregkh>
References: <1708193020-14740-1-git-send-email-ssengar@linux.microsoft.com>
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 <2024021920-wincing-dyslexic-aae1@gregkh>
 <20240219094023.GB32526@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net>
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On Mon, Feb 19, 2024 at 01:40:23AM -0800, Saurabh Singh Sengar wrote:
> On Mon, Feb 19, 2024 at 09:50:54AM +0100, Greg KH wrote:
> > On Sat, Feb 17, 2024 at 10:03:36AM -0800, Saurabh Sengar wrote:
> > > Query the ring buffer size from pre defined table per device.
> > > Keep the size as is if the device doesn't have any preferred
> > > ring size.
> > 
> > What is the "as is" size?
> 
> I will elaborate more here.
> 
> > 
> > > 
> > > Signed-off-by: Saurabh Sengar <ssengar@linux.microsoft.com>
> > > ---
> > >  drivers/uio/uio_hv_generic.c | 7 +++++--
> > >  1 file changed, 5 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/uio/uio_hv_generic.c b/drivers/uio/uio_hv_generic.c
> > > index 20d9762331bd..4bda6b52e49e 100644
> > > --- a/drivers/uio/uio_hv_generic.c
> > > +++ b/drivers/uio/uio_hv_generic.c
> > > @@ -238,6 +238,7 @@ hv_uio_probe(struct hv_device *dev,
> > >  	struct hv_uio_private_data *pdata;
> > >  	void *ring_buffer;
> > >  	int ret;
> > > +	size_t ring_size = hv_dev_ring_size(channel);
> > >  
> > >  	/* Communicating with host has to be via shared memory not hypercall */
> > >  	if (!channel->offermsg.monitor_allocated) {
> > > @@ -245,12 +246,14 @@ hv_uio_probe(struct hv_device *dev,
> > >  		return -ENOTSUPP;
> > >  	}
> > >  
> > > +	if (!ring_size)
> > > +		ring_size = HV_RING_SIZE * PAGE_SIZE;
> > 
> > Why the magic * PAGE_SIZE here?
> > 
> > Where is it documented that ring_size is in pages?
> > 
> > And what happens when PAGE_SIZE is changed?  Why are you relying on that
> > arbritrary value to dictate your buffer sizes to a device that has
> > no relationship with PAGE_SIZE?
> > 
> > Yes, I know you are copying what was there today, but you have the
> > chance to rethink and most importantly, DOCUMENT this decision properly
> > now.
> 
> I agree PAGE_SIZE is not accurate here and we should use HV_HYP_PAGE_SIZE.
> This can be further improved by using VMBUS_RING_SIZE macro.
> 
> However, I propose addressing this improvement in a separate patch, given
> the are significant changes already present in this series.

Add it as a new patch to the series makes sense, thanks!

greg k-h