linux-kernel - Re: [PATCH v2 char-misc 1/1] Drivers: hv: vmbus: Implement Direct Mode for stimer0

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Date:   Thu, 25 Jan 2018 10:59:39 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     mikelley@...rosoft.com
Cc:     linux-kernel@...r.kernel.org, devel@...uxdriverproject.org,
        olaf@...fle.de, apw@...onical.com, vkuznets@...hat.com,
        jasowang@...hat.com, leann.ogasawara@...onical.com,
        marcelo.cerri@...onical.com, sthemmin@...rosoft.com,
        kys@...rosoft.com, x86@...nel.org, jrp@....org
Subject: Re: [PATCH v2 char-misc 1/1] Drivers: hv: vmbus: Implement Direct
 Mode for stimer0

On Mon, Jan 22, 2018 at 03:29:29PM -0700, mikelley@...hange.microsoft.com wrote:
> +/*
> + * If false, we're using the old mechanism for stimer0 interrupts
> + * where it sends a VMbus message when it expires. The old
> + * mechanism is used if Direct Mode is explicitly disabled
> + * by the module parameter, or on older versions of Hyper-V
> + * that don't support Direct Mode. While Hyper-V provides
> + * four stimer's per CPU, Linux uses only stimer0.
> + */
> +static bool direct_mode_enabled = true;
> +module_param(direct_mode_enabled, bool, 0444);
> +MODULE_PARM_DESC(direct_mode_enabled,
> +			"Set to N to disable stimer Direct Mode.");

Ick ick ick.  How is a distro or user supposed to know if/when to enable
this and not to enable it?  This isn't ok, can you please make this
"automatic" to always do the right thing based on what it is running on?

Module parameters are not a good idea as they are impossible to maintain
and document and use over time.  Please never add new ones to the
kernel.

thanks,

greg k-h