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Message-ID: <20071207084559.GA11162@elte.hu> Date: Fri, 7 Dec 2007 09:45:59 +0100 From: Ingo Molnar <mingo@...e.hu> To: Stefano Brivio <stefano.brivio@...imi.it> Cc: Robert Love <rml@...h9.net>, linux-kernel@...r.kernel.org, Dave Jones <davej@...hat.com>, "Rafael J. Wysocki" <rjw@...k.pl>, Michael Buesch <mb@...sch.de>, Thomas Gleixner <tglx@...utronix.de>, Andrew Morton <akpm@...ux-foundation.org>, Len Brown <lenb@...nel.org> Subject: Re: [PATCH] scheduler: fix x86 regression in native_sched_clock * Stefano Brivio <stefano.brivio@...imi.it> wrote: > This patch fixes a regression introduced by: > > commit bb29ab26863c022743143f27956cc0ca362f258c > Author: Ingo Molnar <mingo@...e.hu> > Date: Mon Jul 9 18:51:59 2007 +0200 > > This caused the jiffies counter to leap back and forth on cpufreq > changes on my x86 box. I'd say that we can't always assume that TSC > does "small errors" only, when marked unstable. On cpufreq changes > these errors can be huge. ah, printk_clock() still uses sched_clock(), not jiffies. So it's not the jiffies counter that goes back and forth, it's sched_clock() - so this is a printk timestamps anomaly, not related to jiffies. I thought we have fixed this bug in the printk code already: sched_clock() is a 'raw' interface that should not be used directly - the proper interface is cpu_clock(cpu). Does the patch below help? Ingo -----------------------> Subject: sched: fix CONFIG_PRINT_TIME's reliance on sched_clock() From: Ingo Molnar <mingo@...e.hu> Stefano Brivio reported weird printk timestamp behavior during CPU frequency changes: http://bugzilla.kernel.org/show_bug.cgi?id=9475 fix CONFIG_PRINT_TIME's reliance on sched_clock() and use cpu_clock() instead. Reported-and-bisected-by: Stefano Brivio <stefano.brivio@...imi.it> Signed-off-by: Ingo Molnar <mingo@...e.hu> --- kernel/printk.c | 2 +- kernel/sched.c | 7 ++++++- 2 files changed, 7 insertions(+), 2 deletions(-) Index: linux/kernel/printk.c =================================================================== --- linux.orig/kernel/printk.c +++ linux/kernel/printk.c @@ -680,7 +680,7 @@ asmlinkage int vprintk(const char *fmt, loglev_char = default_message_loglevel + '0'; } - t = printk_clock(); + t = cpu_clock(printk_cpu); nanosec_rem = do_div(t, 1000000000); tlen = sprintf(tbuf, "<%c>[%5lu.%06lu] ", Index: linux/kernel/sched.c =================================================================== --- linux.orig/kernel/sched.c +++ linux/kernel/sched.c @@ -599,7 +599,12 @@ unsigned long long cpu_clock(int cpu) local_irq_save(flags); rq = cpu_rq(cpu); - update_rq_clock(rq); + /* + * Only call sched_clock() if the scheduler has already been + * initialized (some code might call cpu_clock() very early): + */ + if (rq->idle) + update_rq_clock(rq); now = rq->clock; local_irq_restore(flags); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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