linux-kernel - Re: [PATCH v2 0/3] x86/process: Optimize __switch_to

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Date:   Fri, 10 Mar 2017 21:23:43 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Kyle Huey <me@...ehuey.com>
cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>
Subject: Re: [PATCH v2 0/3] x86/process: Optimize __switch_to_xtra()

On Wed, 8 Mar 2017, Kyle Huey wrote:

> On Tue, Feb 28, 2017 at 10:33 AM, Kyle Huey <me@...ehuey.com> wrote:
> > On Tue, Feb 14, 2017 at 12:11 AM, Kyle Huey <me@...ehuey.com> wrote:
> >> GCC generates lousy code in __switch_to_xtra.  This patch series is an
> >> updated version of tglx's patches from last year
> >> (https://lkml.org/lkml/2016/12/15/432) that address review comments.
> >>
> >> Since v1:
> >> Part 1 - x86/process: Optimize TIF checks in __switch_to_xtra()
> >> - READ_ONCE annotations added as requested by Andy Lutomirski
> >>
> >> Part 2 - x86/process: Correct and optimize TIF_BLOCKSTEP switch
> >> - DEBUGCTLMSR_BTF is now modified when either the previous or
> >>   next or both tasks use it, because the MSR is "highly magical".
> >>
> >> Part 3 - x86/process: Optimize TIF_NOTSC switch
> >> - Unchanged
> >>
> >> I didn't introduce a cpufeature for blockstep because that would
> >> add additional overhead compared to the existing code, where it's
> >> generally known at compile time that blockstep is supported. Perhaps
> >> we should just BUG_ON(!arch_has_block_step()) here if we really
> >> care to check anything.
> >>
> >> arch/x86/include/asm/msr-index.h |  1 +
> >> arch/x86/include/asm/tlbflush.h  | 10 ++++++++++
> >> arch/x86/kernel/process.c        | 76 +++++++++++++++++++++++++++++++++++-----------------------------------------
> >> 3 files changed, 46 insertions(+), 41 deletions(-)
> >>
> >
> > Has anyone had a change to look at these?
> 
> Maybe now that the 4.11 merge window is closed? :)

Yes. It's on my radar, but I'm swamped with regressions. Next week should
be more time for that.

Thanks,

	tglx