[gem5-users] Re: How does an out of order pipeline implementation handle instructions (cmp, adds,cmn etc.) which update N,Z,C,V?
Hello Jason, Thank you very much for the quick response. I greatly appreciate it. I will check the source code mentioned. Wishing you a great day. Regards, Tom ___ gem5-users mailing list -- gem5-users@gem5.org To unsubscribe send an email to gem5-users-le...@gem5.org %(web_page_url)slistinfo%(cgiext)s/%(_internal_name)s
[gem5-users] Re: How does an out of order pipeline implementation handle instructions (cmp, adds,cmn etc.) which update N,Z,C,V?
Hi Tom,
On Tue, Mar 29, 2022 at 9:39 AM tomjosekallooran--- via gem5-users <
gem5-users@gem5.org> wrote:
> Hi ,
> This may sound very generic, but i want to try some experiments with the
> out of order implementation. I came across few scenarios, which are listed
> below (any input would be helpful):
> 1. lets consider the following set of instructions (an example which was
> made up):
> Address instr Operands
> 4357136cmp {"x1", "#16"}
> 4357140cmp {"x2", "#16"}
> 4357144bhi {"4387895"}
>
> So if we have two execution units which can execute integer instructions,
> then both "cmp" instruction (4357136 and 4357140) could be issued to the
> execution unit. But an "cmp" instruction will update N,Z,C,V flags which
> inturn are used for evaluating conditional flags (eq_ne, hi_ls, cs_cc etc).
> So, can these two cmp be issued to execution units in the same cycle? If
> so, are the N,Z,C,V for each cmp only updated after inorder commit? How is
> it handled ? (do we use temp registers for holding each N,Z,C,V value?)
>
If I remember correctly, we rename all of the flag registers on each
instruction, and we increase the number of physical registers such that
this renaming is not a bottleneck. In a real processor, I don't think it
would work this way, but it should be OK performance-wise.
>
> 2. In speculative execution, how are stores implemented? do we place them
> into a store buffer and write it to memory once its commited?
>
I think that's correct, at least for x86. In Arm/RISC-V the stores could go
out of order to memory as well. You can check the code in the lsq_unit
files in src/cpu/o3 and poke around for "tso" to see exactly how it's
handled. Someone else may remember better than I do :).
Cheers,
Jason
>
> Any input would be appreciated.
> Regards,
> Tom
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[gem5-users] Upcoming gem5 events! Tutorial, Workshop, and Boot Camp!
Dear all, We wish to make the computer architecture research community aware of several gem5 events occurring over the next 6 months. There will be two events co-located at ISCA 2022 (held in New York, June 18th) -- a 3 hour tutorial, and a 3 hour workshop. In July, there will be a "gem5 Boot Camp", 5 days, July 11 to July 15th, for junior computer architecture researchers to learn how to use gem5 in their projects. Specific event details are shown below. Please relay these details to anyone that may be interested. *ISCA 2022: The gem5 Tutorial* Date: June 18th 2022 (Morning session) Location: ISCA, New York City Webpage: https://www.gem5.org/events/isca-2022#the-4th-gem5-tutorial Registration: Please keep an eye on the ISCA website for registration information https://iscaconf.org/isca2022/ The gem5 tutorial is designed to give computer architecture researchers a "crash course" in using gem5. No prior experience is required and the event is open to anyone wanting to attend. The tutorial will be carried out over the course of a 3 hour session with attendees working from their own laptops. A tentative schedule is shown here: - First hour: Getting started with gem5. This will cover the basics of building a simulation of gem5, from compilation to building full-system simulations using the gem5 standard library. - Second hour: Extending gem5 This will cover how to create your own gem5 simobjects, add your own components to the library, and running simulations with the components you have created. - Third hour: Deeper topics The last hour will cover more advanced topics such as the gem5 memory system and ruby. *ISCA 2022: The gem5 Users' Workshop* Date: June 18th 2022 (Afternoon session) Location: ISCA, New York City Webpage: https://www.gem5.org/events/isca-2022#the-4th-gem5-users-workshop Registration: Please keep an eye on the ISCA website for registration information https://iscaconf.org/isca2022/ Presentation proposal link: https://forms.gle/VZxXsWBniUPGBQdw5 Presentation proposal deadline: April 26th (Notifications sent out by May 9th). The gem5 Users' Workshop will start with a 30 minute keynote presentation by Prof. Jason Lowe-Power titled "Recent Advancements in Mainline gem5 v20.0 – v21.2". This will be followed by a series of 15 minutes presentations. These presentations are an opportunity for users of gem5 to present gem5-related work and foster discussion. Presentations are solicited on a broad range of topics related to gem5. Including, but not limited to: - New gem5 features and models. - Improved models. - Validation against real hardware. - Software Engineering related to gem5. - Experiences using gem5. - Tools, visualizations, data analysis tools, etc. If you wish to present at this year's gem5 Users' workshop, please provide a presentation proposal (a 1 page PDF) here: https://forms.gle/VZxXsWBniUPGBQdw5. The deadline for submitting a presentation proposal is April 26th with acceptance notifications sent out by May 9th. Note: this is an in-person event. Presenters must attend the workshop. *July 2022: The gem5 Boot Camp* Dates: July 11th to July 15th 2022 Location: Davis, California Webpage: https://www.gem5.org/events/boot-camp-2022 Application form: https://forms.gle/3wWPsMDfXyaChmQ68 Application Deadline: May 18th (Notifications sent out by June 1st) The gem5 boot camp is for junior computer architecture researchers, particularly PhD. students, to learn how to use gem5 in their projects. The event will be held over 5 days and will take attendees through all aspects of using the gem5 simulation from setting up basic system simulations, creating components, learning to interpret gem5 stats, all the through to running and modifying simulations comparable to real world systems. This event is free for all accepted attendees. Registration, accommodation and meals will incur no cost. Travel grants will also be available. Those wishing to attend should register using the following form: https://forms.gle/AztSG3mD2BqQ4f967. The deadline for applying is May 18th. Accepted applicants will be notified by June 1st. Kind regards, Bobby -- Dr. Bobby R. Bruce Room 3050, Kemper Hall, UC Davis Davis, CA, 95616 web: https://www.bobbybruce.net ___ gem5-users mailing list -- gem5-users@gem5.org To unsubscribe send an email to gem5-users-le...@gem5.org %(web_page_url)slistinfo%(cgiext)s/%(_internal_name)s
[gem5-users] How does an out of order pipeline implementation handle instructions (cmp, adds,cmn etc.) which update N,Z,C,V?
Hi ,
This may sound very generic, but i want to try some experiments with the out of
order implementation. I came across few scenarios, which are listed below (any
input would be helpful):
1. lets consider the following set of instructions (an example which was made
up):
Address instr Operands
4357136cmp {"x1", "#16"}
4357140cmp {"x2", "#16"}
4357144bhi {"4387895"}
So if we have two execution units which can execute integer instructions, then
both "cmp" instruction (4357136 and 4357140) could be issued to the execution
unit. But an "cmp" instruction will update N,Z,C,V flags which inturn are used
for evaluating conditional flags (eq_ne, hi_ls, cs_cc etc).
So, can these two cmp be issued to execution units in the same cycle? If so,
are the N,Z,C,V for each cmp only updated after inorder commit? How is it
handled ? (do we use temp registers for holding each N,Z,C,V value?)
2. In speculative execution, how are stores implemented? do we place them into
a store buffer and write it to memory once its commited?
Any input would be appreciated.
Regards,
Tom
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