On Wed, 11 Oct 2006 12:54:21 -0700
john stultz <[email protected]> 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?
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