> -----Original Message----- > From: David Miller [mailto:da...@davemloft.net] > Sent: Tuesday, November 3, 2015 7:33 AM > To: KY Srinivasan <k...@microsoft.com> > Cc: eric.duma...@gmail.com; Haiyang Zhang <haiya...@microsoft.com>; > eduma...@google.com; netdev@vger.kernel.org > Subject: Re: [PATCH net-next] net: increase LL_MAX_HEADER if HYPERV_NET > is enabled > > From: KY Srinivasan <k...@microsoft.com> > Date: Tue, 3 Nov 2015 07:59:36 +0000 > > > I have implemented the scheme we had discussed a few weeks ago. In > > this new implementation our driver is NOT requesting addition > > headroom - rndis header and the per packet state is being maintained > > outside of the skb. What I am seeing is that when I have > > LL_MAX_HEADER set to 220 bytes, even though our driver is not using > > the additional head room, I see about a 10% boost in the peak > > performance (about 34 Gbps on a 40Gbps interface). However, when I > > set the LL_MAX_HEADER value to the current default, the peak > > performance drops back to what we currently have (around 31 > > Gbps). In both these cases, there is no reallocation of skb since no > > additional headroom is being requested and yet there is a > > significant difference in performance. I trying to figure out why > > this is the case, your insights will be greatly appreciated. > > It probably has something to do with cache line or data alignment.
Thanks David. I too am leaning towards the same conclusion. Since I am not using any part of skb, it looks like the alignment issue is solved by having a larger LL_MAX_HEADER (220 bytes to be specific). I will do some bare metal testing on the setup we have and report back. Regards, K. Y -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
