Hi Julien, > -----Original Message----- > From: Julien Grall <jul...@xen.org> > Sent: 2022年3月3日 17:15 > To: Wei Chen <wei.c...@arm.com>; Stefano Stabellini > <sstabell...@kernel.org> > Cc: xen-devel@lists.xenproject.org; Bertrand Marquis > <bertrand.marq...@arm.com>; Penny Zheng <penny.zh...@arm.com>; Henry Wang > <henry.w...@arm.com>; nd <n...@arm.com> > Subject: Re: Proposal for Porting Xen to Armv8-R64 - DraftA > > Hi Wei, > > On 03/03/2022 01:35, Wei Chen wrote: > >>> 1. Assembly code for EL1 MPU context_switch > >> > >> This discussion reminds me when KVM decided to rewrite their context > >> switch from assembly to C. The outcome was the compiler is able to do a > >> better job than us when it comes to optimizing. > >> > >> With a C version, we could also share the save/restore code with 32-bit > >> and it is easier to read/maintain. > >> > >> So I would suggest to run some numbers to check if it really worth > >> implementing the MPU save/restore in assembly. > >> > > > > It's interesting to hear KVM guys have similar discussion. Yes, if the > > gains of assembly code is not very obvious, then reusing the code for > 32-bit > > would be more important. As our current platform (FVP) could not do very > > precise performance measurement. I want to keep current assembly code > there, > > when we have a platform that can do such measurement we can have a > thread > > to discuss it. > > I briefly looked at the code, the assembly version is not going to be > trivial to review and we don't know yet whether it has an advantage. So > I would say this should be the inverse here. > > We want the C version first until we can prove the assembly version is > better. > > My gut feeling is we will not need the assembly version. >
Ok, we will rollback to C version. After we will finish the measurements, then we will discuss it again (if the assembly has enough gain). > Cheers, > > -- > Julien Grall
