linux-kernel - RE: [Patch v2 2/3] Drivers: hv: add Azure Blob driver

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Message-ID: <BY5PR21MB15065D01F0AC2DBFE1E40C47CE009@BY5PR21MB1506.namprd21.prod.outlook.com>
Date:   Thu, 1 Jul 2021 17:24:29 +0000
From:   Long Li <longli@...rosoft.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     "longli@...uxonhyperv.com" <longli@...uxonhyperv.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>,
        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>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Hans de Goede <hdegoede@...hat.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        Maximilian Luz <luzmaximilian@...il.com>,
        Mike Rapoport <rppt@...nel.org>,
        Ben Widawsky <ben.widawsky@...el.com>,
        Jiri Slaby <jirislaby@...nel.org>,
        Andra Paraschiv <andraprs@...zon.com>,
        Siddharth Gupta <sidgup@...eaurora.org>,
        Hannes Reinecke <hare@...e.de>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>
Subject: RE: [Patch v2 2/3] Drivers: hv: add Azure Blob driver

> Subject: Re: [Patch v2 2/3] Drivers: hv: add Azure Blob driver
> 
> On Thu, Jul 01, 2021 at 06:58:35AM +0000, Long Li wrote:
> > > Subject: Re: [Patch v2 2/3] Drivers: hv: add Azure Blob driver
> > > > +
> > > > +static struct az_blob_device az_blob_dev;
> > > > +
> > > > +static int az_blob_ringbuffer_size = (128 * 1024);
> > > > +module_param(az_blob_ringbuffer_size, int, 0444);
> > > > +MODULE_PARM_DESC(az_blob_ringbuffer_size, "Ring buffer size
> > > > +(bytes)");
> > >
> > > This is NOT the 1990's, please do not create new module parameters.
> > > Just make this work properly for everyone.
> >
> > The default value is chosen so that it works best for most workloads while
> not taking too much system resources. It should work out of box for nearly all
> customers.
> 
> Please wrap your email lines :(
> 
> Anyway, great, it will work for everyone, no need for this to be changed.
> Then just drop it.
> 
> > But what we see is that from time to time, some customers still want to
> change those values to work best for their workloads. It's hard to predict their
> workload. They have to recompile the kernel if there is no module parameter
> to do it. So the intent of this module parameter is that if the default value
> works for you, don't mess up with it.
> 
> Can you not just determine at runtime that these workloads are overflowing
> the buffer and increase the size of it?  That would be best otherwise you are
> forced to try to deal with a module parameter that is for code, not for devices
> (which is why we do not like module parameters for drivers.)
> 
> Please remove this for now and if you _REALLY_ need it in the future, make it
> auto-tunable.  Or if that is somehow impossible, then make it a per-device
> option, through something like sysfs so that it will work correctly per-device.
> 
> thanks,
> 
> greg k-h

I got your point, will be removing this. 

Thanks,
Long