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Date: Fri, 24 Oct 2014 00:50:58 -0400 (EDT) From: David Miller <davem@...emloft.net> To: david.vrabel@...rix.com Cc: netdev@...r.kernel.org, xen-devel@...ts.xenproject.org, konrad.wilk@...cle.com, boris.ostrovsky@...cle.com Subject: Re: [PATCHv2 net-next] xen-netfront: always keep the Rx ring full of requests From: David Vrabel <david.vrabel@...rix.com> Date: Wed, 22 Oct 2014 11:17:06 +0100 > A full Rx ring only requires 1 MiB of memory. This is not enough > memory that it is useful to dynamically scale the number of Rx > requests in the ring based on traffic rates, because: > > a) Even the full 1 MiB is a tiny fraction of a typically modern Linux > VM (for example, the AWS micro instance still has 1 GiB of memory). > > b) Netfront would have used up to 1 MiB already even with moderate > data rates (there was no adjustment of target based on memory > pressure). > > c) Small VMs are going to typically have one VCPU and hence only one > queue. > > Keeping the ring full of Rx requests handles bursty traffic better > than trying to converge on an optimal number of requests to keep > filled. > > On a 4 core host, an iperf -P 64 -t 60 run from dom0 to a 4 VCPU guest > improved from 5.1 Gbit/s to 5.6 Gbit/s. Gains with more bursty > traffic are expected to be higher. > > Signed-off-by: David Vrabel <david.vrabel@...rix.com> > --- > Changes in v2: > - Keep rxbuf_* sysfs files. Applied. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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