Re: porting reversible on arm/mips

[paawan oza <paawan1982@yahoo.com>]

I am not sure how arm can be drastically slower than x86 ! considering arm 32 bit.
but at the first point, if in some way if prec arch level stuff and abis related framework are in place,
then optimization on the same may lead us to get faster recording like cache implementation and so on.
But I am not sure of any specific reason why on arm it could be very slower, having the same conf as x86. 

Regards,
Oza.


----- Original Message ----
From: Jakob Engblom <jakob@virtutech.com>
To: Sean Chen <sean.chen1234@gmail.com>; Michael Snyder <msnyder@vmware.com>
Cc: paawan oza <paawan1982@yahoo.com>; Hui Zhu <teawater@gmail.com>; gdb@sourceware.org
Sent: Fri, December 11, 2009 1:45:48 PM
Subject: RE: porting reversible on arm/mips

> I was interested in the porting on ARM. But later I found that the
> performance impact on ARM might damage the usage of process record. In
> my experiment, reversible debugging is about 20000x slower, which
> might be endurable on the modern computer. However, ARM target is tens
> of times (or even more if we consider the memory) slower than PC. So
> recording instructions will be very slow, about thousands of
> instructions per second.

I just must pitch in and say that it depends on the simulator.

An advantage to using a full simulator is that you simplify the system and no
longer have to care about OS calls: the OS is just part of the context you save
and reverse.  So the overhead actually goes down compared to native prec.  I
think a reversible ARM simulator can be made to run within a factor of ten of
native speed, easily. 


Best regards,

/jakob

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