Date: Thu, 2 Jun 2016 13:28:01 +0200 From: Roger Pau =?iso-8859-1?Q?Monn=E9?= <royger@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r301197 - head/sys/dev/xen/netfront Message-ID: <20160602112801.yqxgblpmxml6d3uz@mac> In-Reply-To: <201606021114.u52BEQqB047172@repo.freebsd.org> References: <201606021114.u52BEQqB047172@repo.freebsd.org>
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On Thu, Jun 02, 2016 at 11:14:26AM +0000, Roger Pau Monné wrote: > Author: royger > Date: Thu Jun 2 11:14:26 2016 > New Revision: 301197 > URL: https://svnweb.freebsd.org/changeset/base/301197 > > Log: > xen-netfront: always keep the Rx ring full of requests > > This is based on Linux commit 1f3c2eba1e2d866ef99bb9b10ade4096e3d7607c from > David Vrabel: > > 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. > > Reviewed by: Wei Liu <wei.liu2@citrix.com> > Sponsored by: Citrix Systems R&D Differential revision: https://reviews.freebsd.org/D6610
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