Re: [PATCH v4 0/10] bql: Byte Queue Limits
From: Dave Taht <hidden>
Date: 2011-11-29 08:51:44
On Tue, Nov 29, 2011 at 9:43 AM, Eric Dumazet [off-list ref] wrote:
Le mardi 29 novembre 2011 à 09:37 +0100, Dave Taht a écrit :quoted
On Tue, Nov 29, 2011 at 8:23 AM, John Fastabend [off-list ref] wrote:quoted
I wonder if we should consider enabling TSO/GSO per queue or per traffic class on devices that support this. At least in devices that support multiple traffic classes it seems to be a common usage case to put bulk storage traffic (iSCSI) on a traffic class and low latency traffic on a separate traffic class, VoIP for example.VOIP is a drop in the bucket. Turning TSO off on TCP exiting the datacenter (or more specifically), destined anywhere there is potential tx/rx bandwidth disparity would be goooooood.If your cpu is fast enough (and they are most of the time), this makes no difference at all. Instead of consuming 3% of cpu with TSO, you'll consume 10% or 15% and no difference seen on the wire.
Perhaps I don't understand the gross effects of TSO very well, but if you have 100 streams coming from a server, destined to X different destinations, and you FQ to each on a per packet basis, you end up impacting the downstream receive buffers throughout much less than if you send each stream as a burst.
Really, if you want to avoid bursts, TSO has litle to do with them.
If I'm misunderstanding the downstream effects of TSO, I stand corrected.
-- Dave Täht SKYPE: davetaht US Tel: 1-239-829-5608 FR Tel: 0638645374 http://www.bufferbloat.net