* Re: [git pull] scheduler warning fix
2008-11-09 19:23 ` Linus Torvalds
@ 2008-11-09 20:02 ` Ingo Molnar
0 siblings, 0 replies; 3+ messages in thread
From: Ingo Molnar @ 2008-11-09 20:02 UTC (permalink / raw)
To: Linus Torvalds
Cc: linux-kernel, Andrew Morton, Peter Zijlstra, Mike Galbraith
* Linus Torvalds <torvalds@linux-foundation.org> wrote:
>
>
> On Sun, 9 Nov 2008, Ingo Molnar wrote:
> >
> > Please pull the latest sched-fixes-for-linus git tree from:
> >
> > git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip.git sched-fixes-for-linus
> >
> > Fixes a silly build warning that slipped through yesterday, sorry
> > about that.
>
> Whaa?
>
> In file included from /home/torvalds/v2.6/linux/arch/x86/include/asm/timex.h:6,
> from include/linux/timex.h:202,
> from include/linux/jiffies.h:8,
> from include/linux/ktime.h:25,
> from include/linux/timer.h:5,
> from include/linux/workqueue.h:8,
> from include/linux/slub_def.h:11,
> from include/linux/slab.h:124,
> from include/linux/percpu.h:5,
> from include/linux/rcupdate.h:39,
> from include/linux/tracepoint.h:18,
> from include/linux/module.h:19,
> from include/linux/crypto.h:21,
> from arch/x86/kernel/asm-offsets_64.c:7,
> from arch/x86/kernel/asm-offsets.c:4:
> /home/torvalds/v2.6/linux/arch/x86/include/asm/tsc.h: In function ‘vget_cycles’:
> /home/torvalds/v2.6/linux/arch/x86/include/asm/tsc.h:46: error: ‘cycles’ undeclared (first use in this function)
> /home/torvalds/v2.6/linux/arch/x86/include/asm/tsc.h:46: error: (Each undeclared identifier is reported only once
> /home/torvalds/v2.6/linux/arch/x86/include/asm/tsc.h:46: error: for each function it appears in.)
> make[1]: *** [arch/x86/kernel/asm-offsets.s] Error 1
> make: *** [prepare0] Error 2
>
> That makes no sense. You've apparently done some idiotic rebasing of
> a patch that needs to be applied on top of an earlier patch into a
> tree that does _not_ need it, and then send it as a pull request.
>
> What _are_ you doing?
Sigh, sorry - please disregard the pull request.
What happened is that the cleanup patch below introduced that warning
- and this morning i noticed that warning and i thought i introduced
an ugly warning upstream and did a quick fix in that branch - but it
didnt actually need any fixing (and in fact it broke the build).
So upstream is fine and doesnt need any fix.
Ingo
------------------------>
>From cb9e35dce94a1b9c59d46224e8a94377d673e204 Mon Sep 17 00:00:00 2001
From: Ingo Molnar <mingo@elte.hu>
Date: Sat, 8 Nov 2008 20:27:00 +0100
Subject: [PATCH] x86: clean up rdtsc_barrier() use
Impact: cleanup
Move rdtsc_barrier() use to vsyscall_64.c where it's relied on,
and point out its role in the context of its use.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
arch/x86/include/asm/tsc.h | 6 +-----
arch/x86/kernel/vsyscall_64.c | 9 +++++++++
2 files changed, 10 insertions(+), 5 deletions(-)
diff --git a/arch/x86/include/asm/tsc.h b/arch/x86/include/asm/tsc.h
index 9cd83a8..700aeb8 100644
--- a/arch/x86/include/asm/tsc.h
+++ b/arch/x86/include/asm/tsc.h
@@ -44,11 +44,7 @@ static __always_inline cycles_t vget_cycles(void)
if (!cpu_has_tsc)
return 0;
#endif
- rdtsc_barrier();
- cycles = (cycles_t)__native_read_tsc();
- rdtsc_barrier();
-
- return cycles;
+ return (cycles_t)__native_read_tsc();
}
extern void tsc_init(void);
diff --git a/arch/x86/kernel/vsyscall_64.c b/arch/x86/kernel/vsyscall_64.c
index 0b8b669..ebf2f12 100644
--- a/arch/x86/kernel/vsyscall_64.c
+++ b/arch/x86/kernel/vsyscall_64.c
@@ -128,7 +128,16 @@ static __always_inline void do_vgettimeofday(struct timeval * tv)
gettimeofday(tv,NULL);
return;
}
+
+ /*
+ * Surround the RDTSC by barriers, to make sure it's not
+ * speculated to outside the seqlock critical section and
+ * does not cause time warps:
+ */
+ rdtsc_barrier();
now = vread();
+ rdtsc_barrier();
+
base = __vsyscall_gtod_data.clock.cycle_last;
mask = __vsyscall_gtod_data.clock.mask;
mult = __vsyscall_gtod_data.clock.mult;
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