HPET vs other timers

Poul-Henning Kamp phk at phk.freebsd.dk
Sun Jun 3 08:55:56 UTC 2007

In message <46620B92.8020608 at root.org>, Nate Lawson writes:
>Poul-Henning Kamp wrote:
>> Nate Lawson wrote:
>>>> Anyone able to speculate why though?  HPET only reads 32 bits from a
>>>> memory mapped region.  No locking or other requirements.  ACPI_timer
>>>> does multiple IO ops, which according to bde@ are much slower than
>>>> memory reads.  
>> HPET needs to do metastability mitigation and is not "just a read
>> from a memory mapped region".
>If it does, then it's not implemented yet:

It's implemented in hardware, that's why the read is so slow.

Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

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