Messages in this thread | | | Date | Wed, 25 Nov 2009 10:53:56 -0500 | Subject | Re: [tip:sched/core] sched, x86: Optimize branch hint in __switch_to() | From | Brian Gerst <> |
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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.
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