Messages in this thread | | | Date | Wed, 11 Oct 2006 14:26:46 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] i386 Time: Avoid PIT SMP lockups |
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On Wed, 11 Oct 2006 12:54:21 -0700 john stultz <johnstul@us.ibm.com> wrote:
> Andrew: I think this is 2.6.19 material, but probably should go through an -mm or two. > > thanks > -john > > > This patch avoids possible PIT livelock issues seen on SMP systems (and > reported by Andi), by not allowing it as a clocksource on SMP boxes. > > However, since the PIT may no longer be present, we have to properly > handle the cases where SMP systems have TSC skew and fall back from the > TSC. Since the PIT isn't there, it would "fall back" to the TSC again. > So this changes the jiffies rating to 1, and the TSC-bad rating value to > 0. > > Thus you will get the following behavior priority on i386 systems: > > tsc [if present & stable] > hpet [if present] > cyclone [if present] > acpi_pm [if present] > pit [if UP] > jiffies > > Rather then the current more complicated: > tsc [if present & stable] > hpet [if present] > cyclone [if present] > acpi_pm [if present] > pit [if cpus < 4]
Actually <=4, and that matters: there are a lot of 4-ways.
> tsc [if present & unstable] > jiffies >
So this patch has the potential to screw up people who have 2-way or 4-way, no hpet/pm-timer and dodgy TSCs.
Wouldn't it be better to fix the livelock? What's causing it? - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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