lkml.org 
[lkml]   [2009]   [Nov]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    SubjectRe: [tip:sched/core] sched, x86: Optimize branch hint in __switch_to()
    From
    On Wed, Nov 25, 2009 at 4:03 AM, Tim Blechmann <tim@klingt.org> wrote:
    > -----BEGIN PGP SIGNED MESSAGE-----
    > Hash: SHA1
    >
    > On 11/24/2009 06:28 PM, Brian Gerst wrote:
    >> On Tue, Nov 24, 2009 at 11:57 AM, tip-bot for Tim Blechmann
    >> <tim@klingt.org> wrote:
    >>> Commit-ID:  a3a1de0c34de6f5f8332cd6151c46af7813c0fcb
    >>> Gitweb:     http://git.kernel.org/tip/a3a1de0c34de6f5f8332cd6151c46af7813c0fcb
    >>> Author:     Tim Blechmann <tim@klingt.org>
    >>> AuthorDate: Tue, 24 Nov 2009 11:55:15 +0100
    >>> Committer:  Ingo Molnar <mingo@elte.hu>
    >>> CommitDate: Tue, 24 Nov 2009 12:20:04 +0100
    >>>
    >>> sched, x86: Optimize branch hint in __switch_to()
    >>>
    >>> Branch hint profiling on my nehalem machine showed 96%
    >>> incorrect branch hints:
    >>>
    >>>  6548732 174664120  96 __switch_to                    process_64.c
    >>>    406
    >>>  6548745 174565593  96 __switch_to                    process_64.c
    >>>    410
    >>>
    >>> Signed-off-by: Tim Blechmann <tim@klingt.org>
    >>> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
    >>> Cc: Mike Galbraith <efault@gmx.de>
    >>> Cc: Paul Mackerras <paulus@samba.org>
    >>> Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
    >>> Cc: Frederic Weisbecker <fweisbec@gmail.com>
    >>> LKML-Reference: <4B0BBB93.3080307@klingt.org>
    >>> Signed-off-by: Ingo Molnar <mingo@elte.hu>
    >>> ---
    >>>  arch/x86/kernel/process_64.c |    5 ++---
    >>>  1 files changed, 2 insertions(+), 3 deletions(-)
    >>>
    >>> diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
    >>> index ad535b6..d9db104 100644
    >>> --- a/arch/x86/kernel/process_64.c
    >>> +++ b/arch/x86/kernel/process_64.c
    >>> @@ -406,11 +406,10 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
    >>>         * This won't pick up thread selector changes, but I guess that is ok.
    >>>         */
    >>>        savesegment(es, prev->es);
    >>> -       if (unlikely(next->es | prev->es))
    >>> +       if (next->es | prev->es)
    >>>                loadsegment(es, next->es);
    >>> -
    >>>        savesegment(ds, prev->ds);
    >>> -       if (unlikely(next->ds | prev->ds))
    >>> +       if (next->ds | prev->ds)
    >>>                loadsegment(ds, next->ds);
    >>>
    >>>
    >>
    >> 64-bit tasks should have %ds and %es set to null selectors.  The only
    >> time they should be different is for 32-bit tasks.
    >
    > this doesn't seem to be the case on my machine for 96% of the calls ...
    > i am just running 64bit binaries on this machine, no 32bit programs
    > (that i know of (ubuntu karmic amd64))
    >
    > tim

    Some early kernel threads inherited KERNEL_DS from the boot process.
    Patch coming soon.

    --
    Brian Gerst
    --
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2009-11-25 16:57    [W:0.038 / U:0.200 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site