Windows 8 Benchmark Records No Longer Accepted

http://hwbot.org/news/9824_breaking_windows_8_benchmark_results_no_longer_accepted_at_hwbot

by dz0ny • 13 years ago

92 29 13 years ago

hwbot.org

ck2• 13 years ago

Isn't this a problem on any os with cpu "speed stepping" ?

We lose seconds each day on our linux servers and have to use ntpd to stay in sync.

jstanley• 13 years ago

Even 10 seconds a day only amounts to ~0.01% discrepancy. In this article they're reporting up to 7% if I'm reading it correctly.

EDIT: 7% of a day is just over 1h40m.

wbl• 13 years ago

The real-time clock on the motherboard should correct for this.

dz0ny3• 13 years ago

Windows only reads clock at startup and writes it shutdown.

wmf2• 13 years ago

Isn't this a problem on any os with cpu "speed stepping" ?

No. Recent processors have a constant TSC frequency independent of the core frequency, so it's safe to use the TSC to measure real time. Older processors can use the constant-frequency PIT or APIC interval timers.

helloNSA_2• 13 years ago

This has been a significant issue on the windows 8 machines I've handled. It's mitigated somewhat by creating your own scheduled task to more frequently do ntp updates.

I like this guide:

http://www.pretentiousname.com/timesync/

Tomdarkness2• 13 years ago

You modify the BCLK regularly whilst booted into Windows on the different Win 8 machines you handle? Even when overclocking you'd normally not mess with the BCLK unless you are really wanting to push your overclock.

helloNSA_2• 13 years ago

Windows 8 keeps terrible time on laptops or anything else which is trying to power save by varying the clock. I'm not overclocking shit. The OS just doesn't time sync frequently enough. This is why I posted a link about increasing the frequency of time syncs.

This has not been a problem with Windows 7, or XP on the same equipment.

ohwp• 13 years ago

I'm a little confused. Does Windows 8 initially use the real time clock and the MHz as reference without checking if the MHz does change over time?

dz0ny3• 13 years ago

Hardware RTC(special chip on your motherboard) is used at kernel startup. Then software based RTC is used(because you can attach software interrupts to it) and this one drifts if user or system changes main system clock BCLK(sometimes called FSB). It is normal for clock to drift 10s for a period of one week, but not for period of five minutes.

Example from article: By underclocking the BLCK of a Haswell system from 130MHz to 122MHz (-6%), Windows 8 loses 18 seconds over a five minute period; and the inverse applies to overclocking, too. This does not apply for Windows 7, which adjusts itself fine.

mjg59• 13 years ago

The Time Stamp Counter on modern CPUs runs at the same speed regardless of the CPU frequency or idle state, providing that the base clock isn't modified. Under normal use, that's absolutely fine - the OS can calibrate its internal clock against a wall clock timesource at boot time, and then use the TSC (which is very cheap to read, unlike the actual RTC) as a reliable time source.

The problem here is (apparently) that calls that used to cause Windows to read the RTC now give you a TSC-based time instead. If the TSC speed has changed since boot (which should only happen if the user has explicitly changed the CPU base clock, never under normal use) then you have no way to calibrate the OSes idea of time against an actual time source. This is a problem if you're trying to perform accurate benchmarks when under/overclocking.

So yeah, Windows 8 appears to use the CPU TSC without recalibrating when there's a change in TSC tick rate, but that's because the TSC tick rate isn't supposed to change.

ambrop7• 13 years ago

So yeah, Windows 8 appears to use the CPU TSC without recalibrating when there's a change in TSC tick rate, but that's because the TSC tick rate isn't supposed to change.

Right - I'd say that the problem they're having is just a bug in the program they use to change the tick rate at runtime, that is, not making the kernel aware of the change. The article is written as if there is something fundamentally wrong with clock implementation on Win8.

beedogs• 13 years ago

I'm guessing this is another ham-fisted Surface decision that was forced onto the Windows 8 developers.

ape42• 13 years ago

These benchmarking guys are not typical Windows uses. Regular users probably appreciate NTP updates.

masklinn• 13 years ago

This has nothing to do with NTP.

swat535• 13 years ago

So this only affects you if you change BCLK at runtime. Which is something that basically never happens unless you do it yourself explicitly. Dynamic CPU speed only modifies multiplier which does not cause this issue. This is a non-issue for 99% of people, it's only an issue if you are measuring your manhood on an internet website.

redthrowaway• 13 years ago

It's also an issue for anyone who's overclocked their gaming rig, as the computer won't keep accurate time anymore. See this video for a demonstration of that:

http://www.youtube.com/watch?v=brkDKgvXKko&feature=player_em...

Guvante• 13 years ago

Why are you overclocking at run-time vs the simpler BIOS time overclock?

Sure while you are testing stability making run-time changes is nice, but once you know what your system can handle it makes sense to just set that permanently.

Also hopefully a fix will come out soon, since it is already well known that the ratio is allowed to change.

jheriko• 13 years ago

what, the age old problems with the rtc are not handled by windows 8 benchmarking?

i feel this has been noticed nearly 20 years late...

maybe its because i have been a low level guy for a while, but ffs people, know your platform before you start using random features. despite the overriding idea that platform and 'big company' apis are good there are plenty of cases where you can do much better yourself - this is why so much of games industry code is hand rolled.

Windows 8 Benchmark Records No Longer Accepted

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