By: Gionatan Danti (g.danti.delete@this.assyoma.it), April 21, 2012 11:42 am
Room: Moderated Discussions
David Kanter (dkanter@realworldtech.com) on 4/20/12 wrote:
---------------------------
>It's very hard to measure that without using any performance analysis tools. I
>don't disagree that it's a significant hit in performance, but quantifying that is challenging.
Premise: I don't have a Bulldozer chip for testing, so my analisys is based on public results. To me, it seems that ALU performance are quite OK, with < 10% performance loss in some synthetic test:
http://www.ilsistemista.net/index.php/hardware-analysis/24-bulldozer-vs-sandy-bridge-vs-k10-comparison-whats-wrong-with-amd-bulldozer.html?start=5
Also 7-zip decompress benchmark is a strong point of Bulldozer uarch (in comparison to K10.5 cores), denoting higi ALU/memory performance.
>You are correct that the caches are painfully slow, but that's not the reason why.
>Frankly, I don't understand why the L1 is 4 cycles instead of 3. I REALLY don't
>understand why the L2 cache is so slow (20 cycles, really??), because size alone
>doesn't account for it. 12-14 cycles sounds much more reasonable.
Yes, L1 is 4 cycles, but Nehalem has similar L1 latency, yet performs very well. I think that the real problem is the L2: while WCC absorb some latency, the throughput is badly affected by L1 WT desing. Moreover, it seems to me that, while the module's L2 partition has 2xR + 2xW bus, they are only 64 bit wide (compared to Intel design, this is quite low, especially considering single-thread cases).
Some results:
http://www.ilsistemista.net/index.php/hardware-analysis/24-bulldozer-vs-sandy-bridge-vs-k10-comparison-whats-wrong-with-amd-bulldozer.html?start=4
>The fact that the L1 is write through is totally irrelevant to latency and should
>actually improve things because AMD got rid of ECC on the L1. The stores go directly
>to the 4KB write combining cache and then written back to the L2 on a deferred basis.
>
>http://www.realworldtech.com/page.cfm?ArticleID=RWT082610181333&p=9
>
This is true, but the WCC is only 4 KB in size and it can absorbs only limited amount of writes before coalesce them to L2.
>>I still believe BD's biggest problem is its cache >latencies, but the chip as it
>>shipped last year is a badly flawed piece of work.
>
>I think the cache hierarchy overall is definitely one of the biggest culprits.
>Hopefully they will fix things in the future.
>
>DK
I agree. Let see Piledriver...
Regars.
---------------------------
>It's very hard to measure that without using any performance analysis tools. I
>don't disagree that it's a significant hit in performance, but quantifying that is challenging.
Premise: I don't have a Bulldozer chip for testing, so my analisys is based on public results. To me, it seems that ALU performance are quite OK, with < 10% performance loss in some synthetic test:
http://www.ilsistemista.net/index.php/hardware-analysis/24-bulldozer-vs-sandy-bridge-vs-k10-comparison-whats-wrong-with-amd-bulldozer.html?start=5
Also 7-zip decompress benchmark is a strong point of Bulldozer uarch (in comparison to K10.5 cores), denoting higi ALU/memory performance.
>You are correct that the caches are painfully slow, but that's not the reason why.
>Frankly, I don't understand why the L1 is 4 cycles instead of 3. I REALLY don't
>understand why the L2 cache is so slow (20 cycles, really??), because size alone
>doesn't account for it. 12-14 cycles sounds much more reasonable.
Yes, L1 is 4 cycles, but Nehalem has similar L1 latency, yet performs very well. I think that the real problem is the L2: while WCC absorb some latency, the throughput is badly affected by L1 WT desing. Moreover, it seems to me that, while the module's L2 partition has 2xR + 2xW bus, they are only 64 bit wide (compared to Intel design, this is quite low, especially considering single-thread cases).
Some results:
http://www.ilsistemista.net/index.php/hardware-analysis/24-bulldozer-vs-sandy-bridge-vs-k10-comparison-whats-wrong-with-amd-bulldozer.html?start=4
>The fact that the L1 is write through is totally irrelevant to latency and should
>actually improve things because AMD got rid of ECC on the L1. The stores go directly
>to the 4KB write combining cache and then written back to the L2 on a deferred basis.
>
>http://www.realworldtech.com/page.cfm?ArticleID=RWT082610181333&p=9
>
This is true, but the WCC is only 4 KB in size and it can absorbs only limited amount of writes before coalesce them to L2.
>>I still believe BD's biggest problem is its cache >latencies, but the chip as it
>>shipped last year is a badly flawed piece of work.
>
>I think the cache hierarchy overall is definitely one of the biggest culprits.
>Hopefully they will fix things in the future.
>
>DK
I agree. Let see Piledriver...
Regars.
Topic | Posted By | Date |
---|---|---|
Phoronix tests GCC compiler flags and Bulldozer. | I.S.T. | 2012/04/19 02:05 AM |
Single page view? | David Kanter | 2012/04/19 07:59 AM |
Single page view? | wainwright | 2012/04/19 08:22 AM |
Single page view? | slothrop | 2012/04/19 08:23 AM |
Single page view? | David Kanter | 2012/04/19 08:31 AM |
Single page view? | EduardoS | 2012/04/19 02:12 PM |
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Single page view? | Del | 2012/04/19 08:36 AM |
Single page view? | slacker | 2012/04/19 02:56 PM |
Single page view? | Del | 2012/04/22 05:09 AM |
Single page view? | David Kanter | 2012/04/22 08:38 AM |
Single page view? | Del | 2012/04/23 12:22 AM |
Single page view? | Michael S | 2012/04/19 12:30 PM |
Single page view? | Ungo | 2012/04/19 01:25 PM |
Single page view? | Foo_ | 2012/04/19 11:17 PM |
Single page view? | James | 2012/04/20 03:01 AM |
There are ads on the web? | JJB | 2012/04/20 03:32 AM |
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So are you, probably | slacker | 2012/04/21 12:09 PM |
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So are you, probably | iz | 2012/04/22 02:57 PM |
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Aha! | David Kanter | 2012/04/22 02:45 PM |
Aha! | bakaneko | 2012/04/22 07:49 PM |
So are you, probably | iz | 2012/04/22 02:48 PM |
That's not how the business works... | David Kanter | 2012/04/22 04:31 PM |
That's not how the business works... | iz | 2012/04/23 12:49 AM |
So are you, probably | slacker | 2012/04/22 10:31 PM |
back to phoronix | Michael S | 2012/04/23 01:07 AM |
So are you, probably | iz | 2012/04/23 02:29 AM |
Membership at RWT | David Kanter | 2012/04/23 10:24 AM |
So are you, probably | Jukka Larja | 2012/04/27 07:59 AM |
So, what do people think of these numbers> | I.S.T. | 2012/04/19 06:34 PM |
So, what do people think of these numbers> | Linus Torvalds | 2012/04/20 07:34 AM |
So, what do people think of these numbers> | Kira | 2012/04/20 08:18 AM |
So, what do people think of these numbers> | Linus Torvalds | 2012/04/20 09:05 AM |
So, what do people think of these numbers> | Doug Siebert | 2012/04/20 08:00 PM |
So, what do people think of these numbers> | Megol | 2012/04/21 08:05 AM |
So, what do people think of these numbers> | Linus Torvalds | 2012/04/21 12:11 PM |
Most problems are fixed... | Megol | 2012/04/24 06:00 AM |
So, what do people think of these numbers> | bakaneko | 2012/04/20 10:16 AM |
So, what do people think of these numbers> | bakaneko | 2012/04/20 10:37 AM |
So, what do people think of these numbers> | Linus Torvalds | 2012/04/20 12:24 PM |
So, what do people think of these numbers> | Joel | 2012/04/20 01:59 PM |
So, what do people think of these numbers> | Kira | 2012/04/20 02:32 PM |
So, what do people think of these numbers> | EduardoS | 2012/04/20 03:00 PM |
Bulldozer's Oddities. | Joel | 2012/04/20 03:54 PM |
In defense of Bulldozer's Oddities | David Kanter | 2012/04/20 04:32 PM |
In defense of Bulldozer's Oddities | Exophase | 2012/04/20 06:11 PM |
In defense of Bulldozer's Oddities | EduardoS | 2012/04/20 06:46 PM |
In defense of Bulldozer's Oddities | Exophase | 2012/04/20 07:18 PM |
In defense of Bulldozer's Oddities | anonymous | 2012/04/20 10:26 PM |
In defense of Bulldozer's Oddities | JJB | 2012/04/20 10:34 PM |
In defense of Bulldozer's Oddities | imaxx | 2012/04/21 06:21 AM |
In defense of Bulldozer's Oddities | Michael S | 2012/04/21 09:42 AM |
Bulldozer's integer execution units | David Kanter | 2012/04/25 03:29 PM |
Bulldozer's integer execution units | Exophase | 2012/04/26 11:17 AM |
Bulldozer's integer execution units | anonymous | 2012/04/26 02:15 PM |
Bulldozer's integer execution units | EduardoS | 2012/04/26 02:40 PM |
Bulldozer's integer execution units | Foo_ | 2012/04/27 07:21 AM |
Bulldozer's integer execution units | Megol | 2012/04/27 12:38 PM |
Bulldozer's integer execution units | EduardoS | 2012/04/26 02:47 PM |
Bulldozer's integer execution units | Exophase | 2012/04/26 04:02 PM |
Bulldozer's integer execution units | EduardoS | 2012/04/26 05:03 PM |
Bulldozer's integer execution units | Exophase | 2012/04/26 05:24 PM |
Bulldozer's integer execution units | EduardoS | 2012/04/26 06:18 PM |
Bulldozer's cache memory performance | Heikki Kultala | 2012/04/28 12:18 AM |
Bulldozer's cache memory performance | EduardoS | 2012/04/28 09:06 AM |
Bulldozer's integer execution units | David Kanter | 2012/04/26 03:03 PM |
Bulldozer's integer execution units | Exophase | 2012/04/26 03:59 PM |
Bulldozer's integer execution units | David Kanter | 2012/04/26 09:53 PM |
Bulldozer's integer execution units | Exophase | 2012/04/27 07:42 AM |
Bulldozer's integer execution units | David Kanter | 2012/04/27 10:06 AM |
Bulldozer's integer execution units | EduardoS | 2012/04/27 12:27 PM |
K8 divided pipelines? | Paul A. Clayton | 2012/04/27 12:59 PM |
Bulldozer's integer execution units | Michael S | 2012/04/27 03:37 AM |
Bulldozer's integer execution units | Exophase | 2012/04/27 07:33 AM |
Bulldozer's integer execution units | anonymous | 2012/04/27 08:03 AM |
Renaming Flags | Konrad Schwarz | 2012/04/27 02:04 AM |
Renaming Flags | none | 2012/04/27 03:03 AM |
Renaming Flags | Megol | 2012/04/27 11:42 AM |
Bulldozer's integer execution units | hcl64 | 2012/04/27 03:31 PM |
VEX supports 3+ operands. FPU have renaming already(NT) | Megol | 2012/04/28 07:20 AM |
In defense of Bulldozer's Oddities | Linus Torvalds | 2012/04/21 11:26 AM |
Thanks for the lesson | JJB | 2012/04/21 01:23 PM |
Side note.. | Linus Torvalds | 2012/04/21 01:57 PM |
In defense of Bulldozer's Oddities | Exophase | 2012/04/21 11:13 AM |
In defense of Bulldozer's Oddities | EduardoS | 2012/04/21 11:53 AM |
In defense of Bulldozer's Oddities | Gionatan Danti | 2012/04/21 11:42 AM |
In defense of Bulldozer's Oddities | hcl64 | 2012/04/27 04:07 PM |
In defense of Bulldozer's Oddities | David Kanter | 2012/04/28 05:29 AM |
In defense of Bulldozer's Oddities | hcl64 | 2012/04/28 01:44 PM |
In defense of Bulldozer's Oddities | David Kanter | 2012/04/28 08:42 PM |
In defense of Bulldozer's Oddities | hcl64 | 2012/04/28 09:39 PM |
Bulldozer's Oddities. | EduardoS | 2012/04/20 05:05 PM |
Bulldozer's Oddities. | anon | 2012/04/20 07:32 PM |
Bulldozer's Oddities. | EduardoS | 2012/04/21 11:37 AM |
Bulldozer's Oddities. | anon | 2012/04/21 09:16 PM |
Bulldozer's Oddities. | EduardoS | 2012/04/21 09:43 PM |
Bulldozer's Oddities. | anon | 2012/04/22 01:09 AM |
Bulldozer's Oddities. | EduardoS | 2012/04/22 12:57 PM |
Bulldozer's Oddities. | anon | 2012/04/22 03:17 PM |
Bulldozer's Oddities. | EduardoS | 2012/04/22 04:05 PM |
Bulldozer's Oddities. | anon | 2012/04/22 04:42 PM |
Bulldozer's Oddities. | anon | 2012/04/22 05:01 PM |
Bulldozer's Oddities. | EduardoS | 2012/04/22 09:28 PM |
Bulldozer's Oddities. | anon | 2012/04/22 10:05 PM |
Bulldozer's isn't bad. | a reader | 2012/04/21 09:01 AM |
Bulldozer's isn't bad. | Kira | 2012/04/21 10:29 AM |
Bulldozer's isn't bad. | hcl64 | 2012/04/27 04:58 PM |
Bulldozer's isn't bad. | anon | 2012/04/27 05:16 PM |
Bulldozer's isn't bad. | hcl64 | 2012/04/27 06:33 PM |
Bulldozer's isn't bad. | rwessel | 2012/04/27 10:12 PM |
Bulldozer's isn't bad. | EduardoS | 2012/04/28 08:29 AM |
Bulldozer's isn't bad. | EduardoS | 2012/04/28 08:30 AM |
Bulldozer's isn't bad. | Michael S | 2012/04/28 11:36 AM |
Bulldozer is made for SPEC fp | Pelle-48 | 2012/04/21 10:41 AM |
Bulldozer's Oddities. | mpx | 2012/04/22 02:47 AM |
Bulldozer's Oddities. | EduardoS | 2012/04/22 12:57 PM |
Bulldozer's Oddities. | mpx | 2012/04/23 06:04 AM |
Bulldozer's Oddities. | Eric | 2012/04/23 11:33 AM |
Bulldozer's Oddities. | EduardoS | 2012/04/23 01:22 PM |
Bulldozer's Oddities. | Eric | 2012/04/23 06:30 PM |
Bulldozer's Oddities. | hcl64 | 2012/04/27 05:16 PM |
Bulldozer's Oddities. | Y | 2012/04/25 03:34 AM |
Bulldozer's IDIV | Heikki Kultala | 2012/04/27 09:56 PM |
Bulldozer's IDIV | Y | 2012/04/30 12:51 AM |
Bulldozer's IDIV | EduardoS | 2012/04/30 04:39 AM |
Bulldozer's IDIV | P3Dnow | 2012/05/08 12:23 AM |
Bulldozer's IDIV | Exophase | 2012/05/08 06:37 AM |
Bulldozer's Oddities. | EduardoS | 2012/04/23 01:15 PM |
Clustered MT as SMT for high frequency | Paul A. Clayton | 2012/04/20 03:10 PM |
Clustered MT as SMT for high frequency | hcl64 | 2012/04/27 11:56 PM |
Clustered MT as SMT for high frequency | anonymous | 2012/04/28 12:43 AM |
Clustered MT as SMT for high frequency | hcl64 | 2012/04/28 01:59 PM |
Clustered MT as SMT for high frequency | anonymous | 2012/04/28 07:45 PM |
Clustered MT as SMT for high frequency | anon | 2012/04/28 01:13 AM |
Clustered MT as SMT for high frequency | hcl64 | 2012/04/28 02:23 PM |
Clustered MT as SMT for high frequency | anon | 2012/04/28 05:19 PM |
Clustered MT as SMT for high frequency | hcl64 | 2012/04/28 06:58 PM |
Clustered MT as SMT for high frequency | David Kanter | 2012/04/28 05:38 AM |
Guessed meaning of "strong dependency model" | Paul A. Clayton | 2012/04/28 06:24 AM |
Guessed meaning of "strong dependency model" | EduardoS | 2012/04/28 08:46 AM |
*Right meaning* about "strong dependency model" | hcl64 | 2012/04/28 03:59 PM |
Clustered MT as SMT for high frequency | hcl64 | 2012/04/28 03:24 PM |
Clustered MT as SMT for high frequency | anonymous | 2012/04/28 07:50 PM |
Clustered MT as SMT for high frequency | hcl64 | 2012/04/28 08:47 PM |
SNB width | David Kanter | 2012/04/28 08:48 PM |
SNB width | hcl64 | 2012/04/29 01:24 AM |
Clustered MT as SMT for high frequency | David Kanter | 2012/04/28 08:56 PM |
Clustered MT as SMT for high frequency | hcl64 | 2012/04/28 10:44 PM |
SOI, FD vs. PD | David Kanter | 2012/04/29 06:19 AM |
SOI, FD vs. PD | hcl64 | 2012/04/29 04:31 PM |
SOI, FD vs. PD | David Kanter | 2012/04/29 10:26 PM |
SOI, FD vs. PD | hcl64 | 2012/04/30 07:08 AM |
SOI, FD vs. PD | David Kanter | 2012/04/30 08:59 AM |
SOI, FD vs. PD | hcl64 | 2012/04/30 05:10 PM |
SOI, FD vs. PD | David Kanter | 2012/04/30 05:32 PM |
SOI, FD vs. PD | hcl64 | 2012/04/30 09:47 PM |
SOI, FD vs. PD | David Kanter | 2012/05/01 01:24 AM |
SOI, FD vs. PD | hcl64 | 2012/05/01 04:46 AM |
SOI, FD vs. PD | hcl64 | 2012/05/01 05:37 AM |
SOI, FD vs. PD | David Kanter | 2012/05/01 07:19 AM |
SOI, FD vs. PD | hcl64 | 2012/05/01 06:39 AM |
PD-SOI | David Kanter | 2012/05/02 11:22 AM |
SOI, FD vs. PD | slacker | 2012/04/30 07:10 PM |
SOI, FD vs. PD | David Kanter | 2012/04/30 09:16 PM |
SOI, FD vs. PD | slacker | 2012/05/01 09:04 PM |
SOI, FD vs. PD | David Kanter | 2012/05/02 07:19 AM |
SOI, FD vs. PD | zou | 2012/05/02 11:23 AM |
Previous discussion of clustered MT | Paul A. Clayton | 2012/04/28 06:00 AM |
Previous discussion of clustered MT | hcl64 | 2012/04/28 08:38 PM |
Previous discussion of clustered MT | David Kanter | 2012/04/30 03:37 PM |
Previous discussion of clustered MT | hcl64 | 2012/04/30 06:24 PM |
Previous discussion of clustered MT | David Kanter | 2012/04/30 06:40 PM |
Previous discussion of clustered MT | hcl64 | 2012/05/01 08:15 AM |
Latency issues | David Kanter | 2012/05/02 11:01 AM |
So, what do people think of these numbers> | Megol | 2012/04/21 12:57 AM |