Messages in this thread | | | Date | Thu, 16 Feb 2006 10:24:55 -0600 | From | Paul Fulghum <> | Subject | Re: PPP with PCMCIA modem stalls on 2.6.10 or later |
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Kouji Toriatama wrote: > ------------------------------------------------------------------ > Feb 16 23:52:40 moka kernel: receive_chars:flip full:low_latency=0 > Feb 16 23:52:40 moka kernel: receive_chars:flip full:discard char > ------------------------------------------------------------------ > I have got this pair of two lines many times while running the > wget command. ... > With 'low_latency' option in 2.6.15 with your patch, the problem > did not occur and no output from syslog.
Good, the problem is identified: The old flip buffer code can't keep up unless it processes received data directly in the ISR (2.6.9 or 2.6.10+ with low_latency) instead of in scheduled work (2.6.10+ without low_latency).
The discarded receive chars causes dropped frames in ppp_async and stalls in data transfer.
I don't remember the details, but I think it is safe to run low_latency on a uniprocessor.
> I have tried 2.6.16-rc3. With or without 'low_latency' option, > the problem did not occur. It seems to work fine! I will use > 2.6.16-rc3 or later.
Alan's new tty buffering code safely handles high receive rates without data loss, so the low_latency flag is not necessary.
> If you have any additional plan to pin down this problem, I will > try your patch.
The fix is already present in 2.6.16 series, so there is nothing to patch. If you wish to run 2.6.10-2.6.15 you should be able to safely use low_latency on a uniprocessor machine.
-- Paul Fulghum Microgate Systems, Ltd. - 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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