By: Simon Farnsworth (simon.delete@this.farnz.org.uk), October 30, 2016 12:31 pm
Room: Moderated Discussions
juanrga (noemail.delete@this.juanrga.com) on October 29, 2016 10:15 pm wrote:
> Simon Farnsworth (simon.delete@this.farnz.org.uk) on October 28, 2016 6:19 am wrote:
> > juanrga (noemail.delete@this.juanrga.com) on October 28, 2016 2:02 am wrote:
> > >
> > > Essentially the same rule applies upwards and downwards, only parameters vary.
> > >
> > > If your design is optimized for 4GHz and underclocking to 2GHz increases the IPC by less than 5%, then
> > > if your design is optimized for 2GHz, overclocking it to 4GHz will reduce the IPC by a similar amount.
> >
> > The same rule does not apply upward and downward. If it did, I could reliably overclock
> > a Pentium III to 4 GHz, just as I can downclock a modern Intel chip to 800 MHz.
> >
>
> I didn't wrote "the same" but "Essentially the same" and I mentioned explicitly
> that parameters vary (critical path timing, clock skew, jitter...).
If "works" versus "not works" is "essentially the same", then I'd rather not work with any product you engineer.
It's a massive difference - it's not just "parameters vary", it's that you cannot take a circuit with a critical path of 20 FO4 delays, and then clock it so rapidly that it only has 10 FO4 delays in which to stabilise - it will simply fail to operate reliably.
> Simon Farnsworth (simon.delete@this.farnz.org.uk) on October 28, 2016 6:19 am wrote:
> > juanrga (noemail.delete@this.juanrga.com) on October 28, 2016 2:02 am wrote:
> > >
> > > Essentially the same rule applies upwards and downwards, only parameters vary.
> > >
> > > If your design is optimized for 4GHz and underclocking to 2GHz increases the IPC by less than 5%, then
> > > if your design is optimized for 2GHz, overclocking it to 4GHz will reduce the IPC by a similar amount.
> >
> > The same rule does not apply upward and downward. If it did, I could reliably overclock
> > a Pentium III to 4 GHz, just as I can downclock a modern Intel chip to 800 MHz.
> >
>
> I didn't wrote "the same" but "Essentially the same" and I mentioned explicitly
> that parameters vary (critical path timing, clock skew, jitter...).
If "works" versus "not works" is "essentially the same", then I'd rather not work with any product you engineer.
It's a massive difference - it's not just "parameters vary", it's that you cannot take a circuit with a critical path of 20 FO4 delays, and then clock it so rapidly that it only has 10 FO4 delays in which to stabilise - it will simply fail to operate reliably.
Topic | Posted By | Date |
---|---|---|
Neat die area comparison image | Rob | 2016/10/21 05:39 PM |
Neat die area comparison image | anonymou5 | 2016/10/21 06:44 PM |
Neat die area comparison image | Mr. Camel | 2016/10/22 04:58 AM |
Neat die area comparison image | Heikki Kultala | 2016/10/22 05:19 AM |
Neat die area comparison image | Mr. Camel | 2016/10/22 07:10 AM |
Neat die area comparison image | Mr. Camel | 2016/10/22 07:15 AM |
different caches... | Heikki Kultala | 2016/10/22 08:29 AM |
Broadwell includes LLC, just for comparision | anon | 2016/10/22 08:52 AM |
Broadwell includes LLC, just for comparision | juanrga | 2016/10/23 06:09 AM |
Broadwell includes LLC, just for comparision | anon | 2016/10/23 07:25 AM |
Broadwell includes LLC, just for comparision | juanrga | 2016/10/25 09:57 AM |
Broadwell includes LLC, just for comparision | Simon Farnsworth | 2016/10/25 11:03 AM |
Broadwell includes LLC, just for comparision | juanrga | 2016/10/28 02:02 AM |
Broadwell includes LLC, just for comparision | anon | 2016/10/28 04:13 AM |
Broadwell includes LLC, just for comparision | juanrga | 2016/10/29 09:47 PM |
Broadwell includes LLC, just for comparision | Travis | 2016/10/30 06:34 PM |
Broadwell includes LLC, just for comparision | juanrga | 2016/10/31 04:35 AM |
Broadwell includes LLC, just for comparision | Simon Farnsworth | 2016/10/31 04:42 AM |
Broadwell includes LLC, just for comparision | anon | 2016/11/01 12:56 PM |
Broadwell includes LLC, just for comparision | Maynard Handley | 2016/11/01 01:37 PM |
Broadwell includes LLC, just for comparision | anon | 2016/11/01 04:22 PM |
Broadwell includes LLC, just for comparision | Maynard Handley | 2016/11/01 07:30 PM |
Broadwell includes LLC, just for comparision | anon | 2016/11/02 06:15 AM |
Broadwell includes LLC, just for comparision | Maynard Handley | 2016/11/02 09:23 AM |
Broadwell includes LLC, just for comparision | anon | 2016/11/02 11:50 AM |
Broadwell includes LLC, just for comparision | Simon Farnsworth | 2016/11/02 02:48 AM |
Broadwell includes LLC, just for comparision | Simon Farnsworth | 2016/10/28 06:19 AM |
Broadwell includes LLC, just for comparision | juanrga | 2016/10/29 10:15 PM |
Broadwell includes LLC, just for comparision | Simon Farnsworth | 2016/10/30 12:31 PM |
Broadwell includes LLC, just for comparision | Ricardo B | 2016/10/29 05:30 PM |
underclocked is different than designed for low clock speed | Heikki Kultala | 2016/10/25 11:47 PM |
underclocked is different than designed for low clock speed | Maynard Handley | 2016/10/26 10:07 AM |
That wasn't the point | juanrga | 2016/10/28 02:15 AM |
Even without the point you have invalid comparison | Heikki Kultala | 2016/10/28 09:03 AM |
8 wide vs 6 wide | juanrga | 2016/10/29 10:41 PM |
8 wide vs 6 wide | Wilco | 2016/10/30 05:00 AM |
8 wide vs 6 wide | Doug S | 2016/10/30 12:20 PM |
8 wide vs 6 wide | Wilco | 2016/10/30 01:12 PM |
8 wide vs 6 wide | juanrga | 2016/10/30 02:56 PM |
8 wide vs 6 wide | Travis | 2016/10/30 07:13 PM |
8 wide vs 6 wide | juanrga | 2016/10/31 04:55 AM |
8 wide vs 6 wide | anon | 2016/11/01 01:00 PM |
SoftMachines | none | 2016/11/02 03:57 AM |
SoftMachines | David Kanter | 2016/11/02 08:53 AM |
8 wide vs 6 wide | juanrga | 2016/11/03 12:35 PM |
8 wide vs 6 wide | Wilco | 2016/11/03 02:13 PM |
8 wide vs 6 wide | juanrga | 2016/11/03 07:35 PM |
8 wide vs 6 wide | Wilco | 2016/11/04 01:27 PM |
8 wide vs 6 wide | juanrga | 2016/11/04 06:08 PM |
8 wide vs 6 wide | Wilco | 2016/11/06 04:52 AM |
8 wide vs 6 wide | juanrga | 2016/11/06 04:56 PM |
8 wide vs 6 wide | Wilco | 2016/11/07 04:25 AM |
8 wide vs 6 wide | Aaron Spink | 2016/11/04 04:08 PM |
8 wide vs 6 wide | juanrga | 2016/11/04 06:10 PM |
Dunning-Krueger effect | Heikki Kultala | 2016/11/04 03:22 AM |
Dunning-Krueger effect | itsmydamnation | 2016/11/04 02:48 PM |
8 wide vs 6 wide | anon | 2016/11/04 03:38 AM |
8 wide vs 6 wide | juanrga | 2016/11/04 05:05 AM |
8 wide vs 6 wide | anon | 2016/11/04 06:12 AM |
8 wide vs 6 wide | Wilco | 2016/11/04 01:12 PM |
8 wide vs 6 wide | anon | 2016/11/04 02:54 PM |
8 wide vs 6 wide | juanrga | 2016/11/04 05:34 PM |
8 wide vs 6 wide | anon | 2016/11/05 02:14 AM |
8 wide vs 6 wide | juanrga | 2016/11/04 05:39 PM |
8 wide vs 6 wide | Wilco | 2016/11/06 05:15 AM |
8 wide vs 6 wide | juanrga | 2016/11/06 05:06 PM |
8 wide vs 6 wide | Wilco | 2016/11/07 03:45 AM |
8 wide vs 6 wide | David Kanter | 2016/11/07 08:43 PM |
8 wide vs 6 wide | Wilco | 2016/11/08 03:57 AM |
8 wide vs 6 wide | juanrga | 2016/11/14 12:12 PM |
8 wide vs 6 wide | Wilco | 2016/11/14 04:53 PM |
8 wide vs 6 wide | dmcq | 2016/11/15 03:17 AM |
8 wide vs 6 wide | Wilco | 2016/11/15 03:43 AM |
8 wide vs 6 wide | dmcq | 2016/11/15 04:28 AM |
1 µop per instruction is not necessary | Paul A. Clayton | 2016/11/17 12:09 PM |
8 wide vs 6 wide | juanrga | 2016/11/20 06:56 AM |
8 wide vs 6 wide | Wilco | 2016/11/21 05:54 PM |
8 wide vs 6 wide | juanrga | 2016/11/22 08:49 AM |
8 wide vs 6 wide | Wilco | 2016/11/22 03:25 PM |
8 wide vs 6 wide | Wilco | 2016/10/31 03:03 AM |
Skylake can retire 8 uops | David Kanter | 2016/10/31 12:41 AM |
Skylake can retire 8 uops | juanrga | 2016/10/31 04:15 AM |
Skylake can retire 8 uops | Alberto | 2016/11/04 07:22 AM |
8 wide vs 6 wide bogus numbers | Heikki Kultala | 2016/10/30 06:25 AM |
Broadwell includes LLC, just for comparision | anon | 2016/10/26 03:10 AM |
Pushing the hidden agenda | juanrga | 2016/10/28 03:11 AM |
Pushing the hidden agenda | anon | 2016/10/28 04:35 AM |
Neat die area comparison image | David Hess | 2016/10/22 01:26 PM |
Neat die area comparison image | anon2 | 2016/10/22 05:20 PM |
Neat die area comparison image | David Hess | 2016/10/22 10:31 PM |
Neat die area comparison image | anon2 | 2016/10/23 01:50 AM |
Neat die area comparison image | Travis | 2016/10/24 01:26 PM |
Neat die area comparison image | Maynard Handley | 2016/10/24 04:27 PM |
Neat die area comparison image | juanrga | 2016/10/25 10:02 AM |
Neat die area comparison image | David Hess | 2016/10/25 09:59 PM |
Neat die area comparison image | Travis | 2016/10/25 10:22 PM |
Neat die area comparison image | David Hess | 2016/10/25 10:37 PM |
Neat die area comparison image | Travis | 2016/10/30 06:09 PM |
Neat die area comparison image | Gabriele Svelto | 2016/10/26 02:23 AM |
Neat die area comparison image | Doug S | 2016/10/26 08:17 AM |
Neat die area comparison image | Jukka Larja | 2016/10/27 09:28 AM |
Neat die area comparison image | anon | 2016/10/26 03:32 AM |
Neat die area comparison image | juanrga | 2016/10/23 06:29 AM |
Neat die area comparison image | Matthias Waldhauer | 2016/10/22 06:12 AM |
Neat die area comparison image | juanrga | 2016/10/23 05:44 AM |
Neat die area comparison image | Gabriele Svelto | 2016/10/24 02:17 AM |