From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dario Faggioli Subject: Re: Delays on usleep calls Date: Fri, 7 Feb 2014 10:22:16 +0100 Message-ID: <1391764936.9917.58.camel@Solace> References: <1390230336.23576.24.camel@Solace> <52F2AD63.7030109@dornerworks.com> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============3045009814124978284==" Return-path: In-Reply-To: <52F2AD63.7030109@dornerworks.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Robbie VanVossen Cc: Pavlo Suikov , Nate Studer , xen-devel@lists.xen.org List-Id: xen-devel@lists.xenproject.org --===============3045009814124978284== Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="=-tHaWGdfHS6bu6n8Qd0WH" --=-tHaWGdfHS6bu6n8Qd0WH Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On mer, 2014-02-05 at 16:30 -0500, Robbie VanVossen wrote: > On 1/20/2014 10:05 AM, Dario Faggioli wrote: > > What about giving a try to it yourself? I think standardizing on one (a > > set of) specific tool could be a good thing. >=20 > Dario, >=20 Hey! :-) > We thought we would try to get some similar readings for the Arinc653 sch= eduler. > We followed your suggestions from this thread and have gotten some readin= gs for > the following configurations: >=20 That's cool, thanks for doing this and sharing the results. > We used the following command to get results for a 30 millisecond (30,000= us) > interval with 500 loops: >=20 > cyclictest -t1 -i 30000 -l 500 -q >=20 > Results: >=20 > +--------+--------+-----------+-------+-------+-------+ > | Config | Domain | Scheduler | Latency (us) | > | | | | Min | Max | Avg | > +--------+--------+-----------+-------+-------+-------+ > | 1 | 0 | Arinc653 | 20 | 163 | 68 | > | 2 | 0 | Arinc653 | 21 | 173 | 68 | > | 3 | 1 | Arinc653 | 20 | 155 | 75 | > +--------+--------+-----------+-------+-------+-------+ >=20 > It looks like we get negligible latencies for each of these simplistic > configurations. >=20 It looks indeed. You're right, the configuration are simplistic. Yet, as stated before, latency and jitter in scheduling/event response has two major contributors: one is the scheduling algorithm itself, the other is the interrupt/event delivery latency of the platform (HW + HYP + OS). This means that, of course, you need to pick the right scheduler and configure it properly, but there may be other sources of latency and delay, and that is what sets the lowest possible limit, unless you go chasing and fix these 'platform issues'. =46rom your experiments (an from some other numbers I also have) it looks=20 like this lower bound is not terrible in Xen, which is something good to know... So thanks again for taking the time of running the benchmarks and sharing the results! :-D That being said, especially if we compare to baremetal, I think there is some room for improvements (I mean, there always will be an overhead, but still...). Do you, by any chance, have the figures for cyclictest on Linux baremetal too (on the same hardware and kernel, if possible)? Thanks a lot again! Dario --=20 <> (Raistlin Majere) ----------------------------------------------------------------- Dario Faggioli, Ph.D, http://about.me/dario.faggioli Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK) --=-tHaWGdfHS6bu6n8Qd0WH Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iEYEABECAAYFAlL0pcgACgkQk4XaBE3IOsSj/gCcCCOZYJX+4VtkKLeQXaaUY37g qxcAoIFQBv+t+E1G8qr3BY/zesL8bZiJ =5Hts -----END PGP SIGNATURE----- --=-tHaWGdfHS6bu6n8Qd0WH-- --===============3045009814124978284== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel --===============3045009814124978284==--