From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH] Lazy FPU save/restore Date: Sun, 18 Feb 2007 16:25:17 +0200 Message-ID: <45D861CD.4020207@qumranet.com> References: <45D502A1.5000303@codemonkey.ws> <45D81EB6.9010407@qumranet.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel To: Anthony Liguori Return-path: In-Reply-To: <45D81EB6.9010407-atKUWr5tajBWk0Htik3J/w@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org Avi Kivity wrote: > Anthony Liguori wrote: >> The following patch saves the host FPU state and loads the guests FPU >> state if !(CR0.MP == 1 && CR0.TS == 1). >> >> When CR0.MP == 1 && CR0.TS == 1, all FPU activity will generate >> exceptions. OS's use these exceptions to implement lazy FPU loading >> to improve context switch time. Since any FPU activity will generate >> traps, we don't have to worry about the guest modifying the host FPU >> state. >> >> My microbenchmark of choice uses FPU operations so I think the >> results are currently tainted. I've only tested on a 32bit SVM system. >> >> Signed-off-by: Anthony Liguori >> > > Applied, thanks. > ... and reverted. Running an fpu load on both guest and host shows corruption (both on the guest and host). The load is > #include > > void test_fpu() > { > int i; > double f = 0; > > for (i = 0; i < 10000000; ++i) > f += 1 / (1.0 + i); > printf("%20.16f\n", f); > } > > int main(int ac, char **av) > { > while (1) > test_fpu(); > } Compiled statically with -O2 on 64-bit. I don't know what's wrong -- the code looks correct (well, on Intel it wants KVM_GUEST_CR0_MASK to include CR0_MP_MASK and CR0_TS_MASK, but it fails with that too, and it fails on AMD as well). -- error compiling committee.c: too many arguments to function ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys-and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV