On Thu, 8 Nov 2018 at 03:55, Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> wrote: > > This is a refurbished series originally started by by Rik van Riel. The > goal is load the FPU registers on return to userland and not on every > context switch. By this optimisation we can: > - avoid loading the registers if the task stays in kernel and does > not return to userland > - make kernel_fpu_begin() cheaper: it only saves the registers on the > first invocation. The second invocation does not need save them again. > Do you have any performance data? Regards, Wanpeng Li > To access the FPU registers in kernel we need: > - disable preemption to avoid that the scheduler switches tasks. By > doing so it would set TIF_NEED_FPU_LOAD and the FPU registers would be > not valid. > - disable BH because the softirq might use kernel_fpu_begin() and then > set TIF_NEED_FPU_LOAD instead loading the FPU registers on completion. > > v3…v4: > It has been suggested to remove the `initialized' member of the struct > fpu because it should not required be needed with lazy-FPU-restore and > would make the review easier. This is the first part of the series, the > second is basically the rebase of the v3 queue. As a result, the > diffstat became negative (which wasn't the case in previous version) :) > I tried to incorporate all the review comments that came up, some of > them were "outdated" after the removal of the `initialized' member. I'm > sorry should I missed any. > > v1…v3: > v2 was never posted. I followed the idea to completely decouple PKRU > from xstate. This didn't quite work and made a few things complicated. > One obvious required fixup is copy_fpstate_to_sigframe() where the PKRU > state needs to be fiddled into xstate. This required another > xfeatures_mask so that the sanity checks were performed and > xstate_offsets would be computed. Additionally ptrace also reads/sets > xstate in order to get/set the register and PKRU is one of them. So this > would need some fiddle, too. > In v3 I dropped that decouple idea. I also learned that the wrpkru > instruction is not privileged and so caching it in kernel does not work. > Instead I keep PKRU in xstate area and load it at context switch time > while the remaining registers are deferred (until return to userland). > The offset of PKRU within xstate is enumerated at boot time so why not > use it. > > Rik van Riel (5): > x86/fpu: Add (__)make_fpregs_active helpers > x86/fpu: Eager switch PKRU state > x86/fpu: Always store the registers in copy_fpstate_to_sigframe() > x86/fpu: Prepare copy_fpstate_to_sigframe() for TIF_NEED_FPU_LOAD > x86/fpu: Defer FPU state load until return to userspace > > Sebastian Andrzej Siewior (18): > x86/fpu: Use ULL for shift in xfeature_uncompacted_offset() > x86/fpu: Remove fpu->initialized usage in __fpu__restore_sig() > x86/fpu: Remove fpu__restore() > x86/entry/32: Remove asm/math_emu.h include > x86/fpu: Remove preempt_disable() in fpu__clear() > x86/fpu: Always init the `state' in fpu__clear() > x86/fpu: Remove fpu->initialized usage in copy_fpstate_to_sigframe() > x86/fpu: Remove fpu->initialized > x86/fpu: Remove user_fpu_begin() > x86/entry: Remove _TIF_ALLWORK_MASK > x86/fpu: Make __raw_xsave_addr() use feature number instead of mask > x86/fpu: Make get_xsave_field_ptr() and get_xsave_addr() use feature > number instead of mask > x86/pkeys: Make init_pkru_value static > x86/fpu: Only write PKRU if it is different from current > x86/pkeys: Don't check if PKRU is zero before writting it > x86/entry: Add TIF_NEED_FPU_LOAD > x86/fpu: Update xstate's PKRU value on write_pkru() > x86/fpu: Don't restore the FPU state directly from userland in > __fpu__restore_sig() > > Documentation/preempt-locking.txt | 1 - > arch/x86/entry/common.c | 8 ++ > arch/x86/ia32/ia32_signal.c | 17 +-- > arch/x86/include/asm/fpu/api.h | 25 ++++ > arch/x86/include/asm/fpu/internal.h | 149 ++++++---------------- > arch/x86/include/asm/fpu/signal.h | 2 +- > arch/x86/include/asm/fpu/types.h | 9 -- > arch/x86/include/asm/fpu/xstate.h | 6 +- > arch/x86/include/asm/pgtable.h | 19 ++- > arch/x86/include/asm/special_insns.h | 13 +- > arch/x86/include/asm/thread_info.h | 10 +- > arch/x86/include/asm/trace/fpu.h | 8 +- > arch/x86/kernel/fpu/core.c | 181 +++++++++++++-------------- > arch/x86/kernel/fpu/init.c | 2 - > arch/x86/kernel/fpu/regset.c | 24 +--- > arch/x86/kernel/fpu/signal.c | 133 +++++++++----------- > arch/x86/kernel/fpu/xstate.c | 45 ++++--- > arch/x86/kernel/process.c | 2 +- > arch/x86/kernel/process_32.c | 14 +-- > arch/x86/kernel/process_64.c | 11 +- > arch/x86/kernel/signal.c | 17 ++- > arch/x86/kernel/traps.c | 2 +- > arch/x86/kvm/x86.c | 47 ++++--- > arch/x86/math-emu/fpu_entry.c | 3 - > arch/x86/mm/mpx.c | 6 +- > arch/x86/mm/pkeys.c | 15 +-- > 26 files changed, 343 insertions(+), 426 deletions(-) > > git://git.kernel.org/pub/scm/linux/kernel/git/bigeasy/staging.git x86_fpu_rtu_v4 > > Sebastian >
