Messages in this thread | | | Date | Sat, 28 Oct 2006 21:32:18 +0200 | From | Willy Tarreau <> | Subject | Re: AMD X2 unsynced TSC fix? |
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On Sat, Oct 28, 2006 at 12:18:00PM -0700, thockin@hockin.org wrote: > On Sat, Oct 28, 2006 at 09:15:15PM +0200, Willy Tarreau wrote: > > > While gtod is time critical and often appears high on profile lists it is > > > normally not as time critical as you're claiming it is; especially not > > > time critical enough to warrant such radical action. > > > > Yes it was, because the small gain of using a dual core with such > > a workload was clearly lost by that change. IIRC, I reached 25000 > > sessions/s on dual core with TSC if I didn't care about the clock, > > 20000 without TSC, and 18000 on single core+TSC. But with the sniffer, > > it was even worse : I had 500 kpps in dual-core+TSC, 70kpps without > > TSC and 300 kpps with single-core+TSC. Since I had to buy the same > > machines for both uses, this last argument was enough for me to stick > > to a single core. > > Was the problem that they were not synced at poweron or that they would > drift due to power-states?
They resynced at power up, but would constantly drift. I don't even know if it was caused by power states. When the machine was loaded, a single task moving across the cores could see its time jump back and forth several times a second by an offset sometimes close to +2/-2s.
> Did you try running with idle=poll, to avoid ever entering C1 state (hlt)?
Yes, I remember trying such things. I also tried 'nohlt', completely disabling power management, including ACPI, etc... I also tried vanilla kernels as well as severely patched ones, but the problem remained the same in all circumstances, that only 'notsc' could solve.
BTW, I've just found a remain of dmesg capture after boot in case you'd like to look for anything in it.
Regards, Willy
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