netdev - Re: [RFC net-next 00/14] default maximal number of RSS queues in mq drivers

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Date:	Tue, 19 Jun 2012 19:17:12 +0300
From:	"Eilon Greenstein" <eilong@...adcom.com>
To:	"Yuval Mintz" <yuvalmin@...adcom.com>, netdev@...r.kernel.org,
	davem@...emloft.net, "Or Gerlitz" <ogerlitz@...lanox.com>,
	"Divy Le Ray" <divy@...lsio.com>,
	"Jitendra Kalsaria" <jitendra.kalsaria@...gic.com>,
	"Ron Mercer" <ron.mercer@...gic.com>,
	"Anirban Chakraborty" <anirban.chakraborty@...gic.com>,
	"Jeff Kirsher" <jeffrey.t.kirsher@...el.com>,
	"Jon Mason" <jdmason@...zu.us>,
	"Andrew Gallatin" <gallatin@...i.com>,
	"Jon Mason" <mason@...i.com>,
	"Subbu Seetharaman" <subbu.seetharaman@...lex.com>,
	"Sathya Perla" <sathya.perla@...lex.com>,
	"Matt Carlson" <mcarlson@...adcom.com>,
	"Ajit Khaparde" <ajit.khaparde@...lex.com>,
	"Michael Chan" <mchan@...adcom.com>
Subject: Re: [RFC net-next 00/14] default maximal number of RSS queues
 in mq drivers

On Tue, 2012-06-19 at 18:13 +0300, Yuval Mintz wrote:
> Different vendors support different number of RSS queues by default. Today,
> there exists an ethtool API through which users can change the number of
> channels their driver supports; This enables us to pursue the goal of using
> a default number of RSS queues in various multi-queue drivers.
> 
> This RFC intendeds to achieve the above default, by upper-limiting the number
> of interrupts multi-queue drivers request (by default, not via the new API) 
> with correlation to the number of cpus on the machine.
> 
> After examining multi-queue drivers that call alloc_etherdev_mq[s],
> it became evident that most drivers allocate their devices using hard-coded
> values. Changing those defaults directly will most likely cause a regression. 
> 
> However, (most) multi-queue driver look at the number of online cpus when 
> requesting for interrupts. We assume that the number of interrupts the
> driver manages to request is propagated across the driver, and the number
> of RSS queues it configures is based upon it. 
> 
> This RFC modifies said logic - if the number of cpus is large enough, use
> a smaller default value instead. This serves 2 main purposes: 
>  1. A step forward unity in the number of RSS queues of various drivers.
>  2. It prevents wasteful requests for interrupts on machines with many cpus.
> 
> Notice no testing was made on this RFC (other than on the bnx2x driver)
> except for compilation test.
> 
> Drivers identified as multi-queue, handled in this RFC:
> 
> * mellanox mlx4
> * neterion vxge
> * qlogic   qlge
> * intel    igb, igbxe, igbxevf
> * chelsio  cxgb3, cxgb4
> * myricom  myri10ge
> * emulex   benet
> * broadcom tg3, bnx2, bnx2x
> 
> Driver identified as multi-queue, no reference to number of online cpus found,
> and thus unhandled in this RFC:
> 
> * neterion  s2io
> * marvell   mv643xx
> * freescale gianfar
> * ibm       ehea
> * ti        cpmac
> * sun       niu
> * sfc       efx
> * chelsio   cxgb4vf
> 
> Cheers,
> Yuval Mintz
> 
> Cc: Divy Le Ray <divy@...lsio.com>
> Cc: Or Gerlitz <ogerlitz@...lanox.com>
> Cc: Jon Mason <jdmason@...zu.us>
> Cc: Anirban Chakraborty <anirban.chakraborty@...gic.com>
> Cc: Jitendra Kalsaria <jitendra.kalsaria@...gic.com>
> Cc: Ron Mercer <ron.mercer@...gic.com>
> Cc: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
> Cc: Jon Mason <mason@...i.com>
> Cc: Andrew Gallatin <gallatin@...i.com>
> Cc: Sathya Perla <sathya.perla@...lex.com>
> Cc: Subbu Seetharaman <subbu.seetharaman@...lex.com>
> Cc: Ajit Khaparde <ajit.khaparde@...lex.com>
> Cc: Matt Carlson <mcarlson@...adcom.com>
> Cc: Michael Chan <mchan@...adcom.com>

Obviously we need to make the subject line more self-explanatory and
start with the component name followed by colon. We will fix it in the
next version of the patch, but please comment on the content.

Thanks,
Eilon



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