netdev - Re: [PATCH net-next 1/1] hv_netvsc: Properly size the vrss queues

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Message-Id: <20150527.141248.2127547726940414483.davem@davemloft.net>
Date:	Wed, 27 May 2015 14:12:48 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	kys@...rosoft.com
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	devel@...uxdriverproject.org, olaf@...fle.de, apw@...onical.com,
	jasowang@...hat.com
Subject: Re: [PATCH net-next 1/1] hv_netvsc: Properly size the vrss queues

From: "K. Y. Srinivasan" <kys@...rosoft.com>
Date: Tue, 26 May 2015 16:21:09 -0700

> The current algorithm for deciding on the number of VRSS channels is
> not optimal since we open up the min of number of CPUs online and the
> number of VRSS channels the host is offering. So on a 32 VCPU guest
> we could potentially open 32 VRSS subchannels. Experimentation has
> shown that it is best to limit the number of VRSS channels to the number
> of CPUs within a NUMA node. As part of this work introduce a module
> parameter to control the number of sub-channels we would open up as well.
> Here is the new algorithm for deciding on the number of sub-channels we
> would open up:
>         1) Pick the minimum of what the host is offering and what the driver
>            in the guest is specifying via the module parameter.
>         2) Pick the minimum of (1) and the numbers of CPUs in the NUMA
>            node the primary channel is bound to.
> 
> Signed-off-by: K. Y. Srinivasan <kys@...rosoft.com>

No new module parameters, sorry.

You will have to make it such that this can be changed at run time,
and use a generic run-time mechanism to configure this value that any
driver can use.

I will not accept: "this is not possible" or "this is too hard" as a
reason why you have to use a module parameter.

Settings that cannot be set at run time are painful for people who run
large scale operations where resetting entire systems to change a
setting is completely and utterly impractical.
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