| From: | Andres Freund <andres(at)2ndquadrant(dot)com> |
|---|---|
| To: | Abhijit Menon-Sen <ams(at)2ndQuadrant(dot)com> |
| Cc: | Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, pgsql-hackers(at)postgresql(dot)org, Robert Haas <robertmhaas(at)gmail(dot)com> |
| Subject: | Re: What exactly is our CRC algorithm? |
| Date: | 2014-12-30 17:26:41 |
| Message-ID: | 20141230172641.GJ27028@alap3.anarazel.de |
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| Lists: | pgsql-hackers |
On 2014-12-30 21:36:19 +0530, Abhijit Menon-Sen wrote:
> Thanks for spotting that. I had meant to change the test to "& 7". But
> again, now that you mention it, I'm not sure it's necessary. The CRC32*
> instructions don't have the usual SSE alignment requirements, and I see
> that the Linux kernel (among other implementations) process eight bytes
> at a time from the start of the buffer and then process the remaining
> bytes one at a time. I'll do a bit more research and post an update.
I'd done some quick and dirty benchmarking when writing my initial
crc32c POC and I found that four byte aligned accesses were faster than
ones not. But it really just was running it a couple times, nothing more.
Greetings,
Andres Freund
--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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