Messages in this thread | | | Date | Fri, 20 Feb 2015 20:05:54 +0100 | From | Borislav Petkov <> | Subject | Re: [RFC PATCH] x86, fpu: Use eagerfpu by default on all CPUs |
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+ Linus.
I'm sure he'll save something to say about it :-)
On Fri, Feb 20, 2015 at 10:58:15AM -0800, Andy Lutomirski wrote: > We have eager and lazy fpu modes, introduced in: > > 304bceda6a18 x86, fpu: use non-lazy fpu restore for processors supporting xsave > > The result is rather messy. There are two code paths in almost all of the > FPU code, and only one of them (the eager case) is tested frequently, since > most kernel developers have new enough hardware that we use eagerfpu. > > It seems that, on any remotely recent hardware, eagerfpu is a win: > glibc uses SSE2, so laziness is probably overoptimistic, and, in any > case, manipulating TS is far slower that saving and restoring the full > state. > > To try to shake out any latent issues on old hardware, this changes > the default to eager on all CPUs. If no performance or functionality > problems show up, a subsequent patch could remove lazy mode entirely. > > Signed-off-by: Andy Lutomirski <luto@amacapital.net> > --- > arch/x86/kernel/xsave.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kernel/xsave.c b/arch/x86/kernel/xsave.c > index 0de1fae2bdf0..1928c8f34ce5 100644 > --- a/arch/x86/kernel/xsave.c > +++ b/arch/x86/kernel/xsave.c > @@ -637,8 +637,8 @@ static void __init xstate_enable_boot_cpu(void) > prepare_fx_sw_frame(); > setup_init_fpu_buf(); > > - /* Auto enable eagerfpu for xsaveopt */ > - if (cpu_has_xsaveopt && eagerfpu != DISABLE) > + /* Auto enable eagerfpu for everyone */ > + if (eagerfpu != DISABLE) > eagerfpu = ENABLE; > > if (pcntxt_mask & XSTATE_EAGER) { > -- > 2.1.0 > >
-- Regards/Gruss, Boris.
ECO tip #101: Trim your mails when you reply. --
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