Author: Johan de Koning
Date: 18:12:45 08/26/03
Go up one level in this thread
On August 26, 2003 at 11:40:22, Robert Hyatt wrote: >On August 26, 2003 at 03:13:00, Johan de Koning wrote: > >>On August 25, 2003 at 18:28:24, Robert Hyatt wrote: >> >>>On August 25, 2003 at 18:14:15, Sune Fischer wrote: >>> >>>> >>>>>(status quo). >>>> >>>>Right, saw that one too late :) >>>> >>>>>That is exactly what I said. The issue is how many copy/makes have to be >>>>>done per unit of time. Or how many units of time it takes to do a single >>>>>copy/make. Depends on your time scale (1s or 1ns). >>>>> >>>>>A single cpu that will run crafty at 1M nps has a cache-cache and cache-memory >>>>>bandwidth of X bytes/second. A single cpu that runs crafty at 2M nps has >>>>>exactly twice the cache-cache and cache-memory bandwidth and twice the clock >>>>>frequency. A dual-cpu just needs two cpus, but the two cpus give twice the >>>>>cache-cache bandwidth, but _no_ improvement in cache-memory bandwidth. >>>>> >>>>>This was all about memory bandwidth with respect to copy/make. >>>> >>>>Aaah, and here lies our source of disagreement. >>>> >>>>I was always talking about cache to cache, or as Johan wrote "C2C" bandwidth. >>>> >>>>I think the assumptions for make/uncopy to match make/umake is that the stack >>>>fits in cache, or else it will be heavily outgunned, even on a single. >>>> >>>>I doubt anyone disagrees with you there. >>>> >>>>>> >>>>>>You made it sound like 2.4 was much worse than 1, which is just a silly >>>>>>comparison at best. >>>>> >>>>>Clearly 2.4 _is_ much worse than 1. It requires 2.4X the bandwidth. >>>> >>>>Yes _if_ you need to go over the bus. >>>> >>>>-S. >>> >>> >>>My stuff will _never_ fit in 512KB of L2, much less the far smaller L1/trace >>>caches (on the PIV). >>> >>>I am _always_ going to be burning the bus. >> >>Exactly! >>The heavily used stuff will *always* be in the cache. >>For the other stuff it doesn't matter much if the remaining cache space is >>either 31 kB or 28 kB, now does it? >> >>... Johan > > >I don't remember saying that id did matter. You keep saying that copy/make causes problems with cach to memory traffic. Here I was just saying it doesn't, if cache is plenty. > I claimed that for _my_ program, >copy/make burned the bus up and getting rid of it made me go 25% faster. And I suspect this was because of a tiny cache that couldn't even hold the heavily used stuff. ... Johan
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