[Info-vax] Running Alpha VMS under the ES40 emulator

[Johnny Billquist]

On 2013-10-11 16:58, George Cornelius wrote:
> johnwallace4 at yahoo.co.uk wrote:
>
>> Don't know whether readers are all aware, but in AMD64 mode, you gain not just a wider virtual address, which may or may not be a winner, but you also gain twice (roughly) the number of CPU registers, and a few other new featurettes. Twice as many registers is frequently useful, as any PDP11 assembler programmer (or compiler author) will tell you.
>>
>> So a program that doesn't need a 64bit VA *may* get a performance gain simply because it has more registers to play with. On the other hand, in 64bit VA mode, pointers etc take up twice as much cache space. It's not always a guaranteed win to switch to 64bit mode, though it frequently is.
>>
>> Apologies if I'm repeating myself here.
>
> So, for arrays of pointers, or code with lots of 64 bit
> memory references, it can be costly.  But a 64 bit processor
> may have more cache; and ability to address beyond 4 MB can
> be a huge gain, and more so as time goes on, with more and
> more applications just don't cope well with a memory
> constraint of that sort.
>
> I'm finding that what it takes to almost completely freeze
> up my 512 MB / 32 bit Linux system is to leave Mozilla up
> overnight with multiple tabs open.  It pagefaults for what
> seems to be a full 15 minutes at that point, and may still
> be nearly unusable when it all unfreezes [OK, using an
> external Seagate USB3 drive on a USB2 port for paging -
> spinning at an unspecified RPM - but you get the picture].

Probably because you have nightly stuff run by cron which runs over the 
disk. That causes a lot of memory to be used for disk caching, pushing 
all applications out to swap. Which in turn cause a lot of page 
thrashing when you try to do anything, as programs have to fight the OS 
to get a few pages back. There is a big tendency for memory to be used 
as disk cache nowadays...

	Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol