From: John Sigler <linux.kernel@free.fr>
To: linux-rt-users@vger.kernel.org
Cc: Ingo Molnar <mingo@elte.hu>,
linux-kernel@vger.kernel.org, linux-net@vger.kernel.org
Subject: Re: Pin-pointing the root of unusual application latencies
Date: Thu, 26 Jul 2007 17:16:24 +0200 [thread overview]
Message-ID: <46A8BAC8.9000306@free.fr> (raw)
In-Reply-To: <46A5B8E3.4060004@free.fr>
[ Adding linux-net to the mix ]
John Sigler wrote:
> ( check_dektec_in-1095 |#0): new 271 us user-latency.
> ( check_dektec_in-1095 |#0): new 275 us user-latency.
> ( check_dektec_in-1095 |#0): new 290 us user-latency.
> ( check_dektec_in-1095 |#0): new 297 us user-latency.
> ( check_dektec_in-1095 |#0): new 345 us user-latency.
> ( check_dektec_in-1095 |#0): new 358 us user-latency.
> ( check_dektec_in-1095 |#0): new 384 us user-latency.
> ( check_dektec_in-1095 |#0): new 392 us user-latency.
> ( check_dektec_in-1095 |#0): new 395 us user-latency.
> ( check_dektec_in-1095 |#0): new 396 us user-latency.
> ( check_dektec_in-1095 |#0): new 1031 us user-latency.
> ( check_dektec_in-1095 |#0): new 1100 us user-latency.
> ( check_dektec_in-1095 |#0): new 1105 us user-latency.
> ( check_dektec_in-1095 |#0): new 1106 us user-latency.
>
> Here's the function trace for the 1106-µs latency:
>
> http://linux.kernel.free.fr/latency/1106-us-trace.txt
>
> These two lines repeat ~2000 times for ~800 µs:
>
> softirq--4 0.... 272us : __lock_text_start (rt_run_flush)
> softirq--4 0.... 272us : rt_spin_unlock (rt_run_flush)
>
> With a pair of the following in the middle:
>
> softirq--4 0.... 670us : call_rcu (rt_run_flush)
> softirq--4 0D..1 670us : __rcu_advance_callbacks (call_rcu)
Could someone explain why the kernel is "spinning" in rt_run_flush.
http://lxr.linux.no/source/net/ipv4/route.c#L692
What is the kernel trying to do?
Is the kernel in the following loop?
701 for (i = rt_hash_mask; i >= 0; i--) {
702 spin_lock_bh(rt_hash_lock_addr(i));
703 rth = rt_hash_table[i].chain;
704 if (rth)
705 rt_hash_table[i].chain = NULL;
706 spin_unlock_bh(rt_hash_lock_addr(i));
Line 702 would be __lock_text_start (rt_run_flush)
Line 706 would be rt_spin_unlock
Is that correct?
And this would be done 2000 times because rt_hash_mask=2000?
Regards.
prev parent reply other threads:[~2007-07-26 15:16 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <469600F7.3060603@free.fr>
2007-07-23 9:53 ` Pin-pointing the root of unusual application latencies Ingo Molnar
2007-07-23 14:14 ` John Sigler
2007-07-23 16:04 ` Ingo Molnar
2007-07-23 16:44 ` John Sigler
2007-07-24 8:31 ` John Sigler
2007-07-24 9:20 ` John Sigler
2007-07-25 13:04 ` John Sigler
2007-07-25 13:05 ` Ingo Molnar
2007-07-25 13:20 ` John Sigler
2007-07-25 13:38 ` Ingo Molnar
2007-07-25 14:05 ` John Sigler
2007-07-25 15:28 ` Karsten Wiese
2007-07-25 15:46 ` John Sigler
2007-07-25 16:31 ` Karsten Wiese
2007-07-25 17:09 ` Len Brown
2007-07-26 8:35 ` John Sigler
2007-07-26 10:45 ` John Sigler
2007-07-26 12:02 ` John Sigler
2007-07-26 15:16 ` John Sigler [this message]
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