Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.os.linux.advocacy > #108209

Re: Why does Linux need memory management units and cache?

Cross-posted to 3 groups.

Show all headers | View raw

On 20 May 2012, Hadron told this:

> Grant Edwards <invalid@invalid.invalid> writes:
>
>> On 2012-05-19, 7 <email_at_www_at_enemygadgets_dot_com@enemygadgets.com> wrote:
>>> Virtual address space in a nut shell means program counter relative
>>> operation.
>>
>> No, that's not what virtual address space means.

It was interesting to me to learn that the majority of the binaries on
one of my machines, being non-PIC, were running directly on the
1:1-mapped physical memory. I was sure I had virtual memory on that
machine.

> "7" is a COLA troll. He claims to have written a transaction manager
> using the VB clone "gambas" with a mysql server that can monitor and
> process ALL the words financial transactions in real time. Apparently
> its under the GPL. He's a an idiot.

Well, that does depend what the 'processing' is. If it's simple enough,
maybe, but I doubt that all the world's financial transactions will even
fit down one pipe or reasonably-sized set of pipes anymore. Clearly 7
wrote this program in 1970 with the aid of a time machine or doesn't
know just how many trades are executed per day these days.

>>>> Linux doesn't need cache, logically. But Linux systems usually need
>>>> lots of memory, more than can be provided on chip, and access to
>>>> off-chip memories is usually so slow that a cache makes the system
>>>> much faster.
>>>
>>> So a cache could be implemented in software.
>>
>> Not really, no.
>
> Although caches can and are implemented in SW at times.

Caches, yes: I've implemented more than a few myself. The sorts of cache
that sit between the CPU and the RAM can be software-invalidated or
software-tagged but cannot be *implemented* in software. (It would
perhaps be possible to design a system where the cache was controlled
with FPGA logic, thus sort of halfway to software, but that's the
closest you could get I think. To my knowledge nobody has done this,
because it would be both expensive and nearly useless.)

>>> which would use up a lot more software in setting up and managing a
>>> cache.

What does "use up a lot more software" even *mean*? (He clearly hasn't
looked at e.g. the Linux kernel, on which platforms with
software-tagged, software-invalidated or, God forbid, VIPT caches have
*way* more annoying thrashing-about with cache management logic than a
platform with saner semantics like x86 does. FWIW this is the first time
I've ever called x86 sane in any aspect of its design.)

> Another cracker from "7" is that "using the power of Linux" he thinks he
> can write "in assembler" an access path to a distributed multi table
> rdbms record using on the fly selection parameters so thats its orders
> of magnitude faster than using the well configured sql access path. In
> short : he's a fucking idiot.

Well, that's just extreme cluelessness and a massive case of the
Dunning-Kruger effect, I suspect. And/or outright trolling, I suppose,
cola being where old trolls retire to die.

-- 
NULL && (void)

Back to comp.os.linux.advocacy | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Why does Linux need memory management units and cache? 7 <email_at_www_at_enemygadgets_dot_com@enemygadgets.com> - 2012-05-19 13:40 +0100
  Why does Linux need memory management units and cache? Kulin <remailer@reece.net.au> - 2012-05-19 14:26 +0000
  Re: Why does Linux need memory management units and cache? Niklas Holsti <niklas.holsti@tidorum.invalid> - 2012-05-19 19:40 +0300
    Re: Why does Linux need memory management units and cache? 7 <email_at_www_at_enemygadgets_dot_com@enemygadgets.com> - 2012-05-19 18:34 +0100
      Re: Why does Linux need memory management units and cache? Piergiorgio Sartor <piergiorgio.sartor.this.should.not.be.used@nexgo.REMOVETHIS.de> - 2012-05-19 19:44 +0200
        Re: Why does Linux need memory management units and cache? 7 <email_at_www_at_enemygadgets_dot_com@enemygadgets.com> - 2012-05-19 19:57 +0100
          Re: Why does Linux need memory management units and cache? Piergiorgio Sartor <piergiorgio.sartor.this.should.not.be.used@nexgo.REMOVETHIS.de> - 2012-05-19 21:17 +0200
            Re: Why does Linux need memory management units and cache? 7 <email_at_www_at_enemygadgets_dot_com@enemygadgets.com> - 2012-05-20 22:53 +0100
      Re: Why does Linux need memory management units and cache? Grant Edwards <invalid@invalid.invalid> - 2012-05-20 14:42 +0000
        Re: Why does Linux need memory management units and cache? Hadron<hadronquark@gmail.com> - 2012-05-20 16:48 +0200
          Re: Why does Linux need memory management units and cache? Nix <nix-razor-pit@esperi.org.uk> - 2012-05-20 22:19 +0100
            Re: Why does Linux need memory management units and cache? 7 <email_at_www_at_enemygadgets_dot_com@enemygadgets.com> - 2012-05-20 22:55 +0100
              Re: Why does Linux need memory management units and cache? Nix <nix-razor-pit@esperi.org.uk> - 2012-05-21 16:24 +0100
                Re: Why does Linux need memory management units and cache? chrisv <chrisv@nospam.invalid> - 2012-05-21 10:44 -0500
                Re: Why does Linux need memory management units and cache? GreyCloud <mist@cumulus.com> - 2012-05-21 10:51 -0600
                Re: Why does Linux need memory management units and cache? GreyCloud <mist@cumulus.com> - 2012-05-21 10:51 -0600
                Re: Why does Linux need memory management units and cache? Foster <frankfoster50@yahoo.com> - 2012-05-21 12:53 -0400

csiph-web