lkml.org 
[lkml]   [2005]   [Dec]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [patch] latency tracer, 2.6.15-rc7
From
Date
On Fri, 2005-12-30 at 17:02 -0800, Linus Torvalds wrote:
>
> On Fri, 30 Dec 2005, Lee Revell wrote:
> >
> > It seems that the networking code's use of RCU can cause 10ms+
> > latencies:
>
> Hmm. Is there a big jump at the 10ms mark? Do you have a 100Hz timer
> source?
>
> A latency jump at 10ms would tend to indicate a missed wakeup that
> was "picked up" by the next timer tick.

No there are no large jumps, it really seems that this was the network
code causing an RCU callback to drop ~2K routes at once. Specifically
RCU invokes dst_rcu_free 2085 times in a single batch
(call_rcu_bh(&rt->u.dst.rcu_head, dst_rcu_free) is only called from
rt_free() and rt_drop()).

I have found that many of the paths in the network stack that can cause
high latencies can be tuned via sysctls (for example
net.ipv4.route.gc_thresh); this one may be the same.

Lee

-
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/

\
 
 \ /
  Last update: 2005-12-31 02:18    [W:0.138 / U:0.120 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site