Messages in this thread | | | Date | Thu, 3 Sep 2009 13:22:57 +0200 | Subject | Re: PROBLEM: CONFIG_NO_HZ could cause software timeouts | From | Corrado Zoccolo <> |
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Is XIP enabled? It seems that the xip_udelay is not very accurate, and may be the cause of what you are seeing.
On Thu, Sep 3, 2009 at 12:50 PM, Norbert van Bolhuis<nvbolhuis@aimvalley.nl> wrote: > > The problem occurs when e.g. drivers use time_after(jiffes, timeout). > > CONFIG_NO_HZ could make jiffies advance by more than 1. > This is done by: > tick_nohz_update_jiffies->tick_do_update_jiffies64->do_timer > > If drivers use a timeout value of jiffies+1, > "time_after(jiffies, timeout)" will be true after 1 interrupt > (given that it advances jiffies by at least 2). > > This is exactly what happens in cfi_cmdset_0002.c:do_write_buffer > for our case (Powerpc MPC8313, linux-2.6.28, CONFIG_HZ=250, CONFIG_NO_HZ=y). > > do_write_buffer does the following: > unsigned long uWriteTimeout = ( HZ / 1000 ) + 1; > ... > timeo = jiffies + uWriteTimeout; > ... > for (;;) { > ... > if (time_after(jiffies, timeo) && !chip_ready(map, adr)) > break; > if (chip_ready(map, adr)) { > xip_enable(map, chip, adr); > goto op_done; > } > UDELAY(map, chip, adr, 1); > } > /* software timeout */ > ret = -EIO; > opdone: > ... > > I've seen a few software timeouts after the for-loop > looped only 13 times (= 13 us delay, i.s.o. the expected 1 ms). Typically > our NOR flash (S29GL01GP) may need upto ~ 200 us to be ready. > > disabling CONFIG_NO_HZ fixes the problem. > replacing time_after by a for-loop counter to loop max 1000 times > also fixes the problem. > > the latest kernel seems to have the same problem. > > do I miss something here or is this a known problem of CONFIG_NO_HZ ? > -- > 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/ >
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dott. Corrado Zoccolo mailto:czoccolo@gmail.com PhD - Department of Computer Science - University of Pisa, Italy -------------------------------------------------------------------------- The self-confidence of a warrior is not the self-confidence of the average man. The average man seeks certainty in the eyes of the onlooker and calls that self-confidence. The warrior seeks impeccability in his own eyes and calls that humbleness. Tales of Power - C. Castaneda -- 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/
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