Re: [OE-core][dunfell 7/8] qemu: add 34Kf-64tlb fictitious cpu type

Steve Sakoman
2020-10-19T15:48:52Z

On Sun, Oct 18, 2020 at 4:27 AM Richard Purdie
<richard.purdie@linuxfoundation.org> wrote:
>
> On Thu, 2020-10-15 at 04:15 -1000, Steve Sakoman wrote:
> > From: Victor Kamensky <kamensky@cisco.com>
> >
> > In Yocto Project PR 13992 it was reported that qemumips
> > in autobuilder runs almost twice slower then qemumips64 and
> > some times hit time out.
> >
> > Upon investigations of qemu-system with perf, gdb, and
> > SystemTap and comparing qemumips and qemumips64 machines
> > behavior it was noticed that qemu soft mmu code behaves
> > quite different and in case if qemumips tlbwr instruction
> > called 16 times more oftern. It happens that in qemumips64
> > case qemu runs with cpu type that contains 64 TLB, but in case
> > of qemumips qemu runs with cpu type that contains only
> > 16 TLBs.
> >
> > The idea of proposed qemu patch is to introduce fictitious
> > 34Kf-64tlb cpu type that defined exactly as 34Kf but has
> > 64 TLBs, instead of original 16 TLBs.
> >
> > Testing of core-image-full-cmdline:do_testimage with
> > 34Kf-64tlb shows 40% or so test execution real time
> > improvement.
> >
> > Note for future porters of the patch: easiest way to update
> > the patch and be in sync with 34Kf definition is to copy
> > 34Kf machine definition and apply the following changes to
> > it (just change 15 to 63 of CP0C1_MMU bits value)
>
> There is discussion upstream about just changing the tlb to 64 for this
> machine. I'd suggest we hold off this for dunfell until its resolved
> there.

OK, I'll remove these two patches from the pull request.

Steve