Date: Sat, 28 Oct 2006 21:32:18 +0200
From: Willy Tarreau <w@1wt.eu>
To: thockin@hockin.org
Cc: Andi Kleen <ak@suse.de>, Lee Revell <rlrevell@joe-job.com>,
       Luca Tettamanti <kronos.it@gmail.com>, linux-kernel@vger.kernel.org,
       john stultz <johnstul@us.ibm.com>
Subject: Re: AMD X2 unsynced TSC fix?
Message-ID: <20061028193217.GD1709@1wt.eu>
References: <1161969308.27225.120.camel@mindpipe> <1162006081.27225.257.camel@mindpipe> <20061028052837.GC1709@1wt.eu> <200610281137.22451.ak@suse.de> <20061028191515.GA1603@1wt.eu> <20061028191800.GA20701@hockin.org>
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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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