From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joanna Rutkowska Subject: Re: A clocksource question Date: Fri, 12 Mar 2010 22:13:14 +0100 Message-ID: <4B9AAE6A.6050801@invisiblethingslab.com> References: <4B962748.90609@invisiblethingslab.com> <4B9A8FDE.8070506@invisiblethingslab.com> <4B9AB126.1070406@goop.org> <201003122256.02254.tobias.geiger@vido.info> <4B9AB9FE.8070601@goop.org> <4B9AABB9.7030906@invisiblethingslab.com> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============1113390223==" Return-path: In-Reply-To: <4B9AABB9.7030906@invisiblethingslab.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Jeremy Fitzhardinge Cc: Tobias Geiger , xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --===============1113390223== Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enigF6F2A78FCB662DE63A524CEF" This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enigF6F2A78FCB662DE63A524CEF Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable On 03/12/2010 10:01 PM, Joanna Rutkowska wrote: > On 03/12/2010 11:02 PM, Jeremy Fitzhardinge wrote: >> On 03/12/2010 01:56 PM, Tobias Geiger wrote: >>> kbpc2:~# cat >>> /sys/devices/system/clocksource/clocksource0/current_clocksource >>> xen >>> kbpc2:~# cat >>> /sys/devices/system/clocksource/clocksource0/available_clocksource >>> xen >>> kbpc2:~# echo "jiffies" >>> =20 >>>> /sys/devices/system/clocksource/clocksource0/current_clocksource >>>> =20 >>> kbpc2:~# dmesg | tail -1 >>> [ 7898.642404] Override clocksource jiffies is not HRT compatible. >>> Cannot switch >>> while in HRT/NOHZ mode >>> kbpc2:~# >>> >>> Seems like it's not possible to switch to jiffies - however: >>> kbpc2:~# zcat /proc/config.gz | grep NO_HZ >>> # CONFIG_NO_HZ is not set >>> >>> but CONFIG_SCHED_HRTICK=3Dy >>> =20 >> >> Interesting. BTW, does NO_HZ change the behaviour of this? In >> principle NO_HZ should be preferable, and particularly in a virtual >> machine since it should limit the number of timer interrupts. >> >> Joanna, are you using NO_HZ? >> > Yes, I have: > CONFIG_NO_HZ=3Dy >=20 > BTW, FWIW, I'm attaching my kernel config. It's almost the same as the > previously mentioned "Young's Dec23" kernel (the only difference being > some more recent pvops git patches applied and pcifront being enabled a= s > a module). >=20 > While trying to switch from xen source to jiffies source, I got the sam= e > message as Tobias: >=20 > jiffies clocksource is not HRT compatible. Cannot switch while in > HRT/NOHZ mode >=20 > I can definitely say that this previously mentioned warning from hrtime= r > about interrupt being too slow is the marking of the start of all the > troubles. E.g. when I run my Dom0 for some time without starting any > other VMs, the system behaves good, and no warning in dmesg. Only after= > I start a VM, and probably depending on how heavy load it produces, the= > warning appears in Dom0 dmesg and the problem becomes "feelable". And, > depending on what new "delta" is being chosen, the system is either > still usable -- e.g. with a delta like in this case: >=20 > hrtimer: interrupt too slow, forcing clock min delta to 82595226 ns >=20 > which is around 80ms (still the very subtle hiccups can be observed whe= n > you press and hold a key for some time), or totally unusable, if one is= > unlucky, and the "safe" delta got chosen to be something around 0.5s > (which interestingly happens most often in my case). >=20 > The "clocksource tsc unstable" messages trouble me too BTW. They seem t= o > appear before the hrtimer "interrupt too slow" messages. >=20 But this "tsc unstable" message does not seem to be so critical, e.g. I just started my system (xen clocksource) and started a VM, and got the usual hrtimer "slow interrupt" warning, and then all the symptoms started, but there no "tsc unstables" warning in dmesg. However, I previously missed another message, that seem to occur at the very beginning of the system life (before I started any other VMs): Marking TSC unstable due to TSC halts in idle j. --------------enigF6F2A78FCB662DE63A524CEF Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Comment: Using GnuPG with Fedora - http://enigmail.mozdev.org/ iEYEARECAAYFAkuarm8ACgkQORdkotfEW87qKACgyZXS5pGH5HbE2H7R9bkichD6 sTAAoORnIvt9r2q1hMz0JVyXJy2Rdymu =yTCj -----END PGP SIGNATURE----- --------------enigF6F2A78FCB662DE63A524CEF-- --===============1113390223== 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.xensource.com http://lists.xensource.com/xen-devel --===============1113390223==--