On 01/13, Rik van Riel wrote: > > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > On 01/13/2015 12:11 PM, Oleg Nesterov wrote: > > On 01/11, [email protected] wrote: > >> > >> Defer restoring the FPU state, if so desired, until the task > >> returns to userspace. > > > > And I have another concern. > > > > Afaocs with this patch the idle threads will run with TIF_LOAD_FPU > > set but without fpu.has_fpu. > > > > This is fine by itself, but this (performance-wise) breaks > > kernel_fpu_begin() if use_eager_fpu() == T. Please see the > > changelog in 5187b28ff08249ab8a162e8 and note that this patch cc's > > @stable. > > > > Yes, yes, even if I am right we should blame kernel_fpu_begin() and > > other eager_fpu oddities. I tried to start the cleanups/fixes in > > this area some time ago, but they were ignored. > > I suppose we could make kernel_fpu_begin() explicitly point > the cpu's fpu pointer at a special value to indicate that > we are in the middle of a kernel_fpu_begin() / kernel_fpu_end() > session, and should not use the FPU from interrupt context > right now.
Not sure I understand... But yes, I think we need the per-cpu "in_kernel_fpu" and irq_fpu_usable() must die. Please look at http://marc.info/?l=linux-kernel&m=14096628660929 Until then imo this series should try to ensure that kernel_fpu_begin/end will work if interrupted thread is idle task. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
