Hi Sandnon, I suspect the 1 GB extra is a bug. Perhaps Nilay knows?
When it comes to the number of memory controllers, it is simply a convenient way of dealing with the address ranges. For each memory range, we allow interleaving between a number of memory channels. For simplicity, each range thus has its own set of controllers. Going forward I think the right solution here is memory aliasing, but I¹m keen to hear what others have to say about it. In essence we would physically place the memory above the devices, and then alias the first 3 GB to below the devices. Thus, the DRAM would all sit in on contiguous range, and with a single range interleaved across n channels, but the OS would see two ranges. Does that sound ok to everyone? Thanks, Andreas On 15/10/2014 03:51, "sandnon via gem5-users" <gem5-users@gem5.org> wrote: >Hi all, > >When I ran full system mode of gem5 with --mem-size=4GB and >--disk-image=/dist/m5/system/disks/linux-x86.img, it gave me a warn >message that > > > warn: Physical memory size specified is 4GB which is greater than 3GB. > Twice the number of memory controllers would be created. > >And the slave terminal said > > > Memory: 4043292k/5242880k available (3742k kernel code, 150376k >reserved, 1874k data, 232k init) > >It seems gem5 simulated 5GB for me while I requested for 4GB. > >I searched it and found a >[changeset](http://repo.gem5.org/gem5?cmd=changeset;node=fae4550d2103) >which said > > > On the PC platform, the memory region 0xC0000000-0xFFFFFFFF is >reserved for various devices. Hence, if the physical memory size is >greater than 3GB, we need to split it into two parts. > >I still have no idea why gem5 do that even I saw the comments >aforementioned. I know linux kernel will reserve 0xC0000000-0XFFFFFFFF >virtual address for kernel. But I'm not sure if it is related. > >I conclude my questions again > > - Why does gem5 create twice the number of memory controllers while >physical memory size is greater than 3GB > - Why does gem5 simulate 1GB memory more while specified memory size is >greater than 3GB > >--- >Sincerely, >Sandnon >_______________________________________________ >gem5-users mailing list >gem5-users@gem5.org >http://m5sim.org/cgi-bin/mailman/listinfo/gem5-users > -- IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you. ARM Limited, Registered office 110 Fulbourn Road, Cambridge CB1 9NJ, Registered in England & Wales, Company No: 2557590 ARM Holdings plc, Registered office 110 Fulbourn Road, Cambridge CB1 9NJ, Registered in England & Wales, Company No: 2548782 _______________________________________________ gem5-users mailing list gem5-users@gem5.org http://m5sim.org/cgi-bin/mailman/listinfo/gem5-users
