On Sat, Sep 24, 2011 at 9:45 AM, Martijn van Oosterhout
<klep...@svana.org> wrote:
> I think memory accesses are also fantastically expensive, so it's worth
> some effort to optimise that.

This is definitely true.

> I found the Linux kernel document on this topic quite readable. I think
> the main lesson here is that processors track data dependancies (other
> than the Alpha apparently), but not control dependancies.  So in the
> example, the value of i is dependant on num_items, but not via any
> calculation.  IThat control dependancies are not tracked makes some
> sense, since branches depend on flags bit, and just about any
> calculation changes the flag bits, but most of the time these changes
> are not used.

Oh, that's interesting.  So that implies that a read-barrier would be
needed here even on non-Alpha.

Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:

Reply via email to