On 01/18/2018 11:11 AM, Alexey Brodkin wrote:
Hi Vineet,
On Thu, 2018-01-18 at 10:54 -0800, Vineet Gupta wrote:
On 01/18/2018 05:48 AM, Alexey Brodkin wrote:
HS48 core starts with dual-issue enabled but in some cases like
debugging as well as benchmarking it might be useful to disable
dual-issue for a particular run.
Note:
1. To disable dual-issue user has to change a value of a global variable
in target's memory right before start of Linu kernel execution
(most probably via JTAG)
2. Disabling happens very early on boot and to get it back enabled it's
required to restart Linux kernel. I.e. with this change we don't allow
toggling dual-issue state in random moments of run-time
But we need access to a debugger anyways to change this global variable.
If you already have that won't it be better to change the aux register itself
from
the debugger itself.
I don't really see how the global variable way of toggle adds any value here ?
I think there's some sense in a global variable.
1. Not sure if OpenOCD/GDB pair for ARC allows to read/write random AUX regs.
Probably allows but I guess we'll need a new .xml description which lists
EXEC_CTRL
AUX reg. Correct me if I'm wrong here.
Not sure of this a strong argument ...
2. If somebody wants to disable dual-issue persistently (here I mean building
an image
which had dual-issue disabled and there's no need to alter anything after
image loading)
Ok this is more reasonable !
But can we do this in early boot code then. There's a fair bit of code leading up
to where we are doing now so I'd prefer we do it just as we do for disabling L1
caches.
Please note that SLC / IOC are special - as much as I liked to do them super early
- we can't as there's fair bit of code bloat / mem size etc which we don't knwo
that early.
then it's possible just to change a simple and very obvious line in
arch/arc/kernel/setup.c
other than trying to guess what could be good place in sources to stick
that AUX reg write.
Note we don't explicitly do reads of AUX_EXEC_CTRL instead we just use
READ_BCR macro so
for newcomers it might not be immediately obvious what to do and where.
Add the fact that logic of the flag is reversed...
-Alexey
