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From: =?iso-8859-1?Q?Fran=E7ois-Fr=E9d=E9ric_Ozog?= <ff-SpBG2i6TTxU@public.gmane.org>
Subject: Re: Question on the Ring Library
Date: Wed, 4 Dec 2013 14:47:27 +0100
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To: "'Sambath Kumar Balasubramanian'" <sambath.balasubramanian-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
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Hi

On a 10Gbps link, there is a new packet every 650ns on average on each
direction. So handling latency is extremely important.

Traditional "fast" userland mutexes involves system call and scheduling
costs (look at the kernel code: it is "hairy"). I measured difference
between mutex controlled fifo and DPDK controlled fifo on a Xeon =
E5-2680v2,
1867MHz RAM: for times the performance... I consider the cost of a mutex
lock is something close to 400ns on average (well I don't say that it =
always
costs that, but the delays can be not predictable and extremely high - I =
saw
a few ms even if you use isolcpus and precise affinities-). So if you =
plan
to do 10Gbps stuff, I guess polling is the only way to go.

Fran=E7ois-Fr=E9d=E9ric


> -----Message d'origine-----
> De=A0: dev [mailto:dev-bounces-VfR2kkLFssw@public.gmane.org] De la part de Sambath Kumar
> Balasubramanian
> Envoy=E9=A0: mercredi 4 d=E9cembre 2013 12:47
> =C0=A0: dev-VfR2kkLFssw@public.gmane.org
> Objet=A0: [dpdk-dev] Question on the Ring Library
>=20
> Hi,
>=20
>   The ring library seems to be an excellent IPC. But looking at one =
use
> case where the fast path code posts events to event thread for =
example,
the
> event thread will spend some cycles polling the ring rather than =
waiting
> for the event. One approach could be a fast path code basically posts =
the
> event in the ring as is today and there is a background thread that =
polls
> the queues and wakes up the event threads. This is similar to Linux
> SOFTIRQs.The event threads are asynchronous. Is this a fair model to =
avoid
> extra polling CPU cycles by the event threads? Is there any other
> alternatives in dpdk?
>=20
> Regards,
> Sambath