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From: mitchalsup@aol.com (MitchAlsup1)
Newsgroups: comp.arch
Subject: Re: PCIe MSI-X interrupts
Date: Sun, 30 Jun 2024 16:16:01 +0000
Organization: Rocksolid Light
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George Neuner wrote:

> On Fri, 28 Jun 2024 20:26:42 +0000, mitchalsup@aol.com (MitchAlsup1)
> wrote:
>
>>EricP wrote:
>>
>>> MitchAlsup1 wrote:
>>
>>>> Sounds like SNARFing
>>
>>> Write-update depends on broadcasting all writes if that's what snarf
>>> means.
>>
>>General cache coherency policies broadcast a cores address to all
>>caches in the system, and if that cache contains that same cache
>>line, it responds with a SHARED back to requestor, or it invalidates
>>the line. We call this SNOOPing. It works well.
>>
>>SNARF is a term whereby the owner of data broadcasts the data and
>>its address, and any cache containing that line will write the
>>data payload into its cache 9rather than invalidating and then
>>going back and fetching it anew. For certain kinds of data struct
>>SNARF is significantly more efficient than Invalidate-Refetch.
>>A single message around the system performs all the needed updates,
>>instead of 1 invalidate and K fetches.
>>
>>SNARF is almost exclusively used as side-band signals hiding under
>>the cache coherent Interconnect command set.
>>
>>SNARF is almost never available to software. It is more like micro-
>>Architecture talking to other microArchitecture.
>>
>>Also note: µA-to-µA is rarely of line size and often uses physical
>>address bits not available through MMU tables.
>
>
> Stupid question:  why is it called "snarf"?

I don't really know--first heard the term in 1982 as a SNOOP but in
the other direction--instead of taking data away, it put data back.
>
> IIRC, Snoopy (Peanuts) "scarfed" his food.  I don't recall ever seeing
> Snarf (Thundercats) actually eat.