- Als neu kennzeichnen
- Lesezeichen
- Abonnieren
- Stummschalten
- RSS-Feed abonnieren
- Kennzeichnen
- Anstößigen Inhalt melden
FIXED_CTR0 has instructions retired being counted. If the counter is only 40-bit (pre-Nehalem), is there a use of this counter without sampling?
To paraphrase, if all I'm doing is RDPMC on a certain code site, and then RDPMC on another code site, this is bound to overflow right?
Or does that not matter if I always subtract the two numbers and multiply it by negative 1?
1 Lösung
- Als neu kennzeichnen
- Lesezeichen
- Abonnieren
- Stummschalten
- RSS-Feed abonnieren
- Kennzeichnen
- Anstößigen Inhalt melden
Hello halivingston,
There is always the danger of overflowing the counters if they are used in the free-running mode (or sometimes called 'counting mode').
We can estimate how long before the counter will wrap:
Max instructions/sec @ 5 inst/cycle= frequency * 5 inst/cycle
Just for ease of computing say the freq is 2 Ghz then we could get 10 billion (1.0e10)instructions/sec.
A 40 bit counter can count 1,099,511,627,775 (or ~1.1e12) before wrapping.
So, at this example 2GHz frequency and 5 instructions/cycle, we could run about 100 seconds before wrapping.
Of course, some CPUs have a higher frequency but many codes probably don't sustain retiring 5 instructions/cycle.
So... depending on these factors, the wrap around may be longer.
Pat
There is always the danger of overflowing the counters if they are used in the free-running mode (or sometimes called 'counting mode').
We can estimate how long before the counter will wrap:
Max instructions/sec @ 5 inst/cycle= frequency * 5 inst/cycle
Just for ease of computing say the freq is 2 Ghz then we could get 10 billion (1.0e10)instructions/sec.
A 40 bit counter can count 1,099,511,627,775 (or ~1.1e12) before wrapping.
So, at this example 2GHz frequency and 5 instructions/cycle, we could run about 100 seconds before wrapping.
Of course, some CPUs have a higher frequency but many codes probably don't sustain retiring 5 instructions/cycle.
So... depending on these factors, the wrap around may be longer.
Pat
Link kopiert
4 Antworten
- Als neu kennzeichnen
- Lesezeichen
- Abonnieren
- Stummschalten
- RSS-Feed abonnieren
- Kennzeichnen
- Anstößigen Inhalt melden
Try to consultIntel Manuals.
- Als neu kennzeichnen
- Lesezeichen
- Abonnieren
- Stummschalten
- RSS-Feed abonnieren
- Kennzeichnen
- Anstößigen Inhalt melden
Hello halivingston,
There is always the danger of overflowing the counters if they are used in the free-running mode (or sometimes called 'counting mode').
We can estimate how long before the counter will wrap:
Max instructions/sec @ 5 inst/cycle= frequency * 5 inst/cycle
Just for ease of computing say the freq is 2 Ghz then we could get 10 billion (1.0e10)instructions/sec.
A 40 bit counter can count 1,099,511,627,775 (or ~1.1e12) before wrapping.
So, at this example 2GHz frequency and 5 instructions/cycle, we could run about 100 seconds before wrapping.
Of course, some CPUs have a higher frequency but many codes probably don't sustain retiring 5 instructions/cycle.
So... depending on these factors, the wrap around may be longer.
Pat
There is always the danger of overflowing the counters if they are used in the free-running mode (or sometimes called 'counting mode').
We can estimate how long before the counter will wrap:
Max instructions/sec @ 5 inst/cycle= frequency * 5 inst/cycle
Just for ease of computing say the freq is 2 Ghz then we could get 10 billion (1.0e10)instructions/sec.
A 40 bit counter can count 1,099,511,627,775 (or ~1.1e12) before wrapping.
So, at this example 2GHz frequency and 5 instructions/cycle, we could run about 100 seconds before wrapping.
Of course, some CPUs have a higher frequency but many codes probably don't sustain retiring 5 instructions/cycle.
So... depending on these factors, the wrap around may be longer.
Pat
- Als neu kennzeichnen
- Lesezeichen
- Abonnieren
- Stummschalten
- RSS-Feed abonnieren
- Kennzeichnen
- Anstößigen Inhalt melden
Isn't there a better answer I am more precise?
http://deportedirecto.es/categories.php?category=Mujer
Homepage
Business in Italy
Work from home
http://deportedirecto.es/categories.php?category=Mujer
Homepage
Business in Italy
Work from home
Homepage (5) |
- Als neu kennzeichnen
- Lesezeichen
- Abonnieren
- Stummschalten
- RSS-Feed abonnieren
- Kennzeichnen
- Anstößigen Inhalt melden
In what way would you like the answer to be more precise?

Antworten
Themen-Optionen
- RSS-Feed abonnieren
- Thema als neu kennzeichnen
- Thema als gelesen kennzeichnen
- Diesen Thema für aktuellen Benutzer floaten
- Lesezeichen
- Abonnieren
- Drucker-Anzeigeseite