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From: Andy Glew "newsgroup at on 8 Aug 2010 14:43
On 8/6/2010 10:10 AM, Nick Maclaren wrote:
> In article<94ad8368-5fbd-4c8a-a016-492a2a6ab11f(a)f42g2000yqn.googlegroups.com>,
> MitchAlsup<MitchAlsup(a)aol.com> wrote:
>>
>>>> On Intel P6-family machines - i.e. the majority of computers>=3D laptop=
>> s
>>>> and desktops and servers (can't say majority of machines) - TLB misses
>>>> are handled by a hardware state machine that walks the page tables
>>>> during OOO execution. =A0They don't drain the pipeline. =A0They have OOO
>>>> semantics.
>>>
>>> Interesting. =A0Intel is following IBM, then. =A0Many of the other
>>> architectures I have used have not done that.
>>
>> Do ANY OoO machines with hardware TLB reloaders DRAIN the pipeline to
>> refill a TLB?
>
> I doubt it - that would be plain bonkers! But quite a few machines
> simply raised an interrupt on a TLB miss and left the rest to the
> software. As you will remember, that was dogma in the early days
> of the new RISC architectures!
>
> I can no longer remember the results of my timing tests, but I had
> some intended to check that systems weren't TOO catastrophic on
> such things. I can remember quite a lot being dire including, if
> I recall, post-P6 Intel systems.

P6 made TLB misses less expensive than branch mispredictions. At least
on some situations.

Itanium may not have done so.

P6 family machines always had this property, but the overall efficiency
has fluctuated.

Virtual machines have made TLB misses expensive again, but fixups are
happening.
From: Nick Maclaren on 8 Aug 2010 15:47
In article <fuWdnR9KTaFAZ8PRnZ2dnUVZ_gudnZ2d(a)giganews.com>,
Andy Glew <"newsgroup at comp-arch.net"> wrote:
>>
>> I can no longer remember the results of my timing tests, but I had
>> some intended to check that systems weren't TOO catastrophic on
>> such things. I can remember quite a lot being dire including, if
>> I recall, post-P6 Intel systems.
>
>P6 made TLB misses less expensive than branch mispredictions. At least
>on some situations.

As I said, I can't remember.

>Virtual machines have made TLB misses expensive again, but fixups are
>happening.

Just like the IBM System/370 again :-)


Regards,
Nick Maclaren.
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