netdev - Re: [PATCH net-next] net: introduce netdevice gso_min

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Date:	Mon, 06 Oct 2014 05:22:55 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Amir Vadai <amirv@...lanox.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, netdev@...r.kernel.org,
	Yevgeny Petrilin <yevgenyp@...lanox.com>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Ido Shamay <idos@...lanox.com>
Subject: Re: [PATCH net-next] net: introduce netdevice gso_min_segs attribute

On Mon, 2014-10-06 at 05:17 -0700, Eric Dumazet wrote:
> On Mon, 2014-10-06 at 09:41 +0300, Amir Vadai wrote:
> > On 10/5/2014 8:11 PM, Eric Dumazet wrote:
> > > From: Eric Dumazet <edumazet@...gle.com>
> > > 
> > > Some TSO engines might have a too heavy setup cost, that impacts
> > > performance on hosts sending small bursts (2 MSS per packet).
> > > 
> > > This patch adds a device gso_min_segs, allowing drivers to set
> > > a minimum segment size for TSO packets, according to the NIC
> > > performance.
> > > 
> > > Tested on a mlx4 NIC, this allows to get a ~110% increase of
> > > throughput when sending 2 MSS per packet.
> > > 
> > 
> > Amazing!
> > 
> > Shouldn't there be a netif_set_gso_min_size() too?
> 
> Good point, I'll add it in v2, thanks !

Well, no... I thought you were speaking of an hypothetical
netif_set_gso_{max|min}_segs()

But we don't have it. : Drivers simply change dev->gso_max_segs

drivers/net/ethernet/freescale/fec_main.c:3058:         ndev->gso_max_segs = FEC_MAX_TSO_SEGS;
drivers/net/ethernet/marvell/mv643xx_eth.c:3120:        dev->gso_max_segs = MV643XX_MAX_TSO_SEGS;
drivers/net/ethernet/marvell/mvneta.c:3057:     dev->gso_max_segs = MVNETA_MAX_TSO_SEGS;
drivers/net/ethernet/sfc/efx.c:2300:    net_dev->gso_max_segs = EFX_TSO_MAX_SEGS;

So my mlx4 patch was simply doing

	dev->gso_min_segs = MLX4_MIN_TSO_SEGS;


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