Date: Fri, 5 Sep 2014 10:44:05 -0400 From: John Baldwin <jhb@freebsd.org> To: Konstantin Belousov <kostikbel@gmail.com> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r270850 - in head/sys: i386/i386 i386/include i386/isa x86/acpica Message-ID: <201409051044.05853.jhb@freebsd.org> In-Reply-To: <20140905084305.GN2737@kib.kiev.ua> References: <201408301748.s7UHmc6H059701@svn.freebsd.org> <3070015.668SIdAzOX@ralph.baldwin.cx> <20140905084305.GN2737@kib.kiev.ua>
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On Friday, September 05, 2014 4:43:05 am Konstantin Belousov wrote: > On Thu, Sep 04, 2014 at 10:50:25PM -0400, John Baldwin wrote: > > On Tuesday, September 02, 2014 06:41:27 PM Konstantin Belousov wrote: > > > On Tue, Sep 02, 2014 at 11:00:57AM -0400, John Baldwin wrote: > > > > I thought about that. I could easily make a parallel array, or perhaps > > > > use a separate 'susppcb' structure that includes a pcb and the savefpu > > > > union and change susppcbs to be an array of those. Which do you prefer? > > > > If we want to move some state out of the PCB on amd64 into this, then a > > > > separate struct for susppcbs might be the sanest. > > > > > > Yes, separate structure seems to be a way forward. > > > > Please see www.freebsd.org/~jhb/patches/susppcb.patch Note that I moved > > fpususpend() out into a C function on amd64 so that resumectx() could still > > operate on just a pcb. This also makes savectx and resumectx more symmetric > > and matches what I ended up doing on i386. This is tested for suspend and > > resume on both i386 and amd64. > > The implementation of fpuresume() in C is definitely an improvement. > > You only moved the fpu context to the susppcb, I think this is good for > now, we will want to move other bits later. > > Do we need to keep pcb layout for KBI compat ? I remember that pcb > size is asserted to properly fit into pcpu area for percpu zones. > But why keep the layout ? I.e. moving all padding bits to the end. I wasn't sure. I thought the padding was there for ABI reasons. If we don't need KBI compat, I would much rather consolidate all the padding at the end. > There is one weird detail, not touched by your patch. Amd64 resume > path calls initializecpu(), while i386 does not. I do not see any > use for the call, the reload of CRX registers by trampoline/resumectx > should already set everything to working state. E.g., enabling XMM > in CR4 after fpu state is restored looks strange. I can test that. > Overall, it looks fine. Do you prefer to have alloc_fpusave() on i386 ? Well, it might be nice to have XSAVE on i386. I'm not sure if Intel has any 32-bit only chips planned that will use AVX or MPX, etc. If they are, then I do think AVX on i386 would be nice to have. Barring XSAVE I think we can just use a static savefpu on i386 for now. We might also consider removing support for 486sx CPUs and requiring an on-CPU FPU for i386. If we do that we might able to use a common fpu.c which would be even nicer. -- John Baldwin
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