Re: [Gems-users] When to invalidate instruction (trace) cache?

["Eirik Bakke" <ebakke@xxxxxxxxxxxxx>]

Sorry, Mike, my mistake -- we are indeed implementing the Trace Cache in Opal, not Ruby.

 

An equivalent question is "When is the correct time to flush lines in the instruction cache to account for newly loaded instructions?". The Trace Cache is just an extension of the instruction cache that needs to flush at the same times.

 

-- Eirik

---

From: gems-users-bounces@xxxxxxxxxxx [mailto:gems-users-bounces@xxxxxxxxxxx] On Behalf Of Mike Marty
Sent: 9. desember 2007 21:10
To: Gems Users
Subject: Re: [Gems-users] When to invalidate instruction (trace) cache?

I can't tell you when the correct time to flush the trace cache 
is.  That is a research area I'm not very familiar with.

I could be 
completely wrong, but it might make sense to completely implement a trace cache 
in Opal instead of Ruby.  

--Mike

On Dec 8, 2007 11:32 PM, Eirik Bakke <ebakke@xxxxxxxxxxxxx> wrote:

We are implementing/simulating a Trace Cache [1] in ruby. While an
instruction cache stores sequences of instructions in the order they are
stored in memory (static order), the Trace Cache stores sequences of
instructions in the order they are fetched and executed (dynamic order).
Most of our changes are limited to "opal/system/pseq.C".

Since the Trace Cache is indeed a cache that is supposed to reflect data in
memory (instructions), it must be flushed every now and then. In particular,
it must be flushed whenever instructions are loaded for the first time (into
a location which potentially could have contained other instructions
before). According to [2], SPARC requires that a FLUSH instruction is issued
before newly loaded instructions are executed, to flush the instruction
cache. If this is the case, we can simply flush entries in the Trace Cache
at the same time. However, [3] seems to indicate that there are several
other more obscure methods that software may use to achieve the same effect.

When is the correct time to flush instructions from an instruction or trace
cache? Where is the best spot to hook into this in opal?

Eirik & Evan

[1] www.tinker.ncsu.edu/ericro/publications/conference_MICRO-29_rbs.pdf
[2] http://bugs.opensolaris.org/view_bug.do?bug_id=1238184
[3] http://www.sparc.org/standards/sparc64.errata.txt

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