> I think I had come across that problem too but I am sure
> that one of my patches will fix that. Probably this one

Yes -- that's what I meant by "commits related to 3dd04381".
So, let's start with this small area.

> Yes, I can submit it via gerrit.
> As a kernel developer, I am more used to mailing list based reviews
> but feel free to let me know what works best for you.

Gerrit is the procedure currently used by the gem5 community.  Even though I 
personally find it non-ideal, it is kind of a given for the foreseeable future, 
and I think the optimal scenario (within the realistic choices) would be if you 
started upstreaming using that procedure.  The other alternative, of which I 
was afraid before I initially wrote to you, would have been if you had 
abandoned the project or had no time/energy to do the rebasing / pushing / 
working with the review, in that case I was thinking about just taking your 
patches and putting them on Gerrit myself but I can see a whole number of 
reasons to avoid this.


-----"Sandipan Das" <[email protected]> wrote: -----
To: "Boris Shingarov" <[email protected]>
From: "Sandipan Das" <[email protected]>
Date: 02/03/2021 01:30PM
Cc: [email protected], "Pratik Rajesh Sampat" <[email protected]>, 
"Kajol Jain" <[email protected]>, "Gautham R. Shenoy" 
<[email protected]>, "gem5 Developer List" <[email protected]>
Subject: Re: [gem5-dev] Re: Upstreaming power-gem5

Hello Boris,

On 03/02/21 2:34 am, Boris Shingarov wrote:
> Hi Sandipan,
> 
>> This makes it possible
>> to run both 32-bit and 64-bit big and little endian PowerPC binaries
>> in SE mode. If its okay with you, we can start by working on trying to
>> get these changes reviewed and merged first.
> 
> Yes, yes!  This aligns very well with both what sequence I think is the most 
> realistic technically, and with my project's priorities.
> 

Great!

>> You can find them here: [develop-power]
> 
> Some of these commits just scream as the perfect first candidates, for 
> example 
> https://urldefense.proofpoint.com/v2/url?u=https-3A__github.com_sandip4n_gem5_commit_3dd0438159d67fe2b5bcc777b43046fdca90f6b9&d=DwICaQ&c=sPZ6DeHLiehUHQWKIrsNwWp3t7snrE-az24ztT0w7Jc&r=ecC5uu6ubGhPt6qQ8xWcSQh1QUJ8B1-CG4B9kRM0nd4&m=wgWrcP9-wt5oZuq9SWs5UbL4CH93tpVcax1mrsrf0hU&s=qRcEv2oabPve_Q2GdbmZOqMVBxL32Co3y4ROuJevXDA&e=
>  and related.  Because right now the Decoder is in a really sad state, 
> crashing even on simple, perfectly valid programs (and that's even within BE, 
> 32-bit SE), see for example 
> https://urldefense.proofpoint.com/v2/url?u=https-3A__gem5.atlassian.net_browse_GEM5-2D819&d=DwICaQ&c=sPZ6DeHLiehUHQWKIrsNwWp3t7snrE-az24ztT0w7Jc&r=ecC5uu6ubGhPt6qQ8xWcSQh1QUJ8B1-CG4B9kRM0nd4&m=wgWrcP9-wt5oZuq9SWs5UbL4CH93tpVcax1mrsrf0hU&s=ST81CURwY4zbSASQ6L3PKNAA0FC7ia8-GQTVzzunqEs&e=.
>   So, how about we start from that one?  How would you like to proceed -- do 
> you want to submit on Gerrit using the regular process a
 nd I will review it?
> 

I think I had come across that problem too but I am sure
that one of my patches will fix that. Probably this one:
https://urldefense.proofpoint.com/v2/url?u=https-3A__github.com_sandip4n_gem5_commit_3b0203e63d892c94fd0e67cfe79f5e6662504c4a&d=DwICaQ&c=sPZ6DeHLiehUHQWKIrsNwWp3t7snrE-az24ztT0w7Jc&r=ecC5uu6ubGhPt6qQ8xWcSQh1QUJ8B1-CG4B9kRM0nd4&m=wgWrcP9-wt5oZuq9SWs5UbL4CH93tpVcax1mrsrf0hU&s=GAbuvqL0DsFG6QcbNsVo4liY1x1U2DR8YE0ekWQDYE8&e=

>> this has been a hobby/side project and hence, the biggest
>> challenge for us has been finding spare cycles
> 
> At my day job at LabWare, I write JIT compilers, and the development 
> technology is centered around simulation -- so I can't draw a bright line 
> where gem5 stops being a "side" project and becomes part of the "main" 
> project because the latter depends on it.  But it does mean that I naturally 
> have more timeslices for some aspects of gem5 than for other aspects.
>>> So, in order for external UARTs like 8250 to be
>> used for console interactions, we currently use some hacks
>> which I am sure are not quite upstreamable
> 
> Yeah, we are in the same boat here.
> I, too, have a long queue of hacks to gem5 which I did just to enable some 
> experiments with the JIT compiler; they've been waiting *years* that I rework 
> them into "real" patches to go upstream -- but that stage of work is very 
> slow and painful labour.
> 

Sounds interesting. I have minimal experience with JIT
compilers having worked on the Linux kernel's in-built
eBPF JIT compilers. Have peeked into Qemu's TCG too.

On that note, are there any plans to add a JIT engine
to gem5? Since gem5 supports checkpoints, uninteresting
parts of a program can be run in JITed mode to speed
things up.

>> The FS mode changes depend on 64-bit support but aside from that,
>> it also needs a fair amount
> 
> What scares me every time I think about FS, is that it will need coordinating 
> across projects/communities (Kernel, OPAL, ...) where I don't have a lot of 
> background in.  Well, let's worry about FS when the time comes.
> 

The folks that I work with here at IBM LTC can assist us
with that. Besides, like we agreed, lets start with SE
mode.


- Sandipan
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