From: Ian Campbell <Ian.Campbell@citrix•com>
To: David Vrabel <david.vrabel@citrix•com>
Cc: Wei Liu <wei.liu2@citrix•com>, <netdev@vger•kernel.org>,
<xen-devel@lists•xenproject.org>,
Jonathan Davies <jonathan.davies@citrix•com>
Subject: Re: [Xen-devel] [RFC PATCHv1 net-next] xen-netback: always fully coalesce guest Rx packets
Date: Tue, 20 Jan 2015 11:21:48 +0000 [thread overview]
Message-ID: <1421752908.10440.224.camel@citrix.com> (raw)
In-Reply-To: <54BD408A.6080405@citrix.com>
On Mon, 2015-01-19 at 17:36 +0000, David Vrabel wrote:
> On 13/01/15 14:30, Wei Liu wrote:
> > On Tue, Jan 13, 2015 at 02:05:17PM +0000, David Vrabel wrote:
> >> Always fully coalesce guest Rx packets into the minimum number of ring
> >> slots. Reducing the number of slots per packet has significant
> >> performance benefits (e.g., 7.2 Gbit/s to 11 Gbit/s in an off-host
> >> receive test).
> >>
> >
> > Good number.
> >
> >> However, this does increase the number of grant ops per packet which
> >> decreases performance with some workloads (intrahost VM to VM)
> >
> > Do you have figures before and after this change?
>
> Some better (more rigorous) results done by Jonathan Davies shows no
> regressions with full coalescing even without the grant copy
> optimization, and a big improvement to single stream receive.
>
> baseline Full coalesce
> Interhost aggregate 24 Gb/s 24 Gb/s
> Interhost VM receive 7.2 Gb/s 11 Gb/s
> Intrahost single stream 14 Gb/s 14 Gb/s
> Intrahost aggregate 34 Gb/s 34 Gb/s
>
> We do not measure the performance of dom0 to guest traffic but my ad-hoc
> measurements suggest this may be 5-10% slower. I don't think this is a
> very important use case though.
If you are updating your dom0 kernel to take advantage of this
improvement and you care about dom0->domU performance too then also
updating your Xen at the same is not a huge deal, I think. Or at least I
don't consider it a blocker for making progress (certainly not progress
of the order of 50% improvements!).
> So...
>
> >> /unless/ grant copy has been optimized for adjacent ops with the same
> >> source or destination (see "grant-table: defer releasing pages
> >> acquired in a grant copy"[1]).
> >>
> >> Do we need to retain the existing path and make the always coalesce
> >> path conditional on a suitable version of Xen?
>
> ...I think the answer to this is no.
Agreed.
> >> ---
> >> drivers/net/xen-netback/common.h | 1 -
> >> drivers/net/xen-netback/netback.c | 106 ++-----------------------------------
> >> 2 files changed, 3 insertions(+), 104 deletions(-)
> >
> > Love the diffstat!
>
> Yes, it's always nice when you delete code and it goes faster... :)
Full-Ack to that ;-)
Ian.
next prev parent reply other threads:[~2015-01-20 11:21 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-01-13 14:05 [RFC PATCHv1 net-next] xen-netback: always fully coalesce guest Rx packets David Vrabel
2015-01-13 14:30 ` Wei Liu
2015-01-19 17:36 ` [Xen-devel] " David Vrabel
2015-01-20 11:21 ` Ian Campbell [this message]
2015-01-20 11:23 ` Ian Campbell
2015-01-20 11:34 ` Ian Campbell
2015-01-20 11:38 ` David Vrabel
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