Re: top hogs CPU in 2.6: kallsyms_lookup is very slow

[Denis Vlasenko]

On Friday 17 September 2004 15:10, William Lee Irwin III wrote:
> On Thu, Sep 16, 2004 at 02:57:08PM +0300, Denis Vlasenko wrote:
> >> Did the kallsyms patches reduce the cpu overhead from get_wchan()? I take
> >> this to mean reducing HZ to 100 did not alleviate the syscall problems?
> >> How do microbenchmarks fare, e.g. lmbench?
> 
> On Fri, Sep 17, 2004 at 02:21:15PM +0300, Denis Vlasenko wrote:
> > 2x3 lmbench runs. HZ=100, configs attached.
> > Context switching - times in microseconds - smaller is better
> > -------------------------------------------------------------------------
> > Host                 OS  2p/0K 2p/16K 2p/64K 8p/16K 8p/64K 16p/16K 16p/64K
> >                          ctxsw  ctxsw  ctxsw ctxsw  ctxsw   ctxsw   ctxsw
> > --------- ------------- ------ ------ ------ ------ ------ ------- -------
> > hunter    Linux 2.6.9-r   31.9   64.0  120.8  115.7  322.2   136.0   356.4
> > hunter    Linux 2.6.9-r   29.1   47.2   76.7  102.3  321.5   136.0   354.2
> > hunter    Linux 2.6.9-r   29.3   56.0  144.5  101.9  305.5   145.3   351.0
> > hunter    Linux 2.4.27-   19.8   39.4  190.3   77.8  368.0   104.1   401.5
> > hunter    Linux 2.4.27-   19.7   30.9  105.0   87.2  316.9   107.2   359.9
> > hunter    Linux 2.4.27-   19.5   34.6   95.5   74.3  279.1   109.5   325.0
> 
> Bizarre; context switching latency is actually one of the 2.6
> scheduler's strong points AFAIK. This generally needs NMI's to
> instrument as the critical sections here have interrupts disabled.
> Someone more knowledgable regarding the i8259A PIC may have ideas about
> how to go about arranging for NMI-based profiling on a system such as
> yours. I presume this is a Pentium "Classic", not Pentium Pro.

Yes. Ther is no Pentium 66 MMX on this planet.

> Alan, any ideas?
> 
> 
> On Fri, Sep 17, 2004 at 02:21:15PM +0300, Denis Vlasenko wrote:
> > *Local* Communication latencies in microseconds - smaller is better
> > ---------------------------------------------------------------------
> > Host                 OS 2p/0K  Pipe AF     UDP  RPC/   TCP  RPC/ TCP
> >                         ctxsw       UNIX         UDP         TCP conn
> > --------- ------------- ----- ----- ---- ----- ----- ----- ----- ----
> > hunter    Linux 2.6.9-r  31.9 129.8 230.                             
> > hunter    Linux 2.6.9-r  29.1 130.1 244.                             
> > hunter    Linux 2.6.9-r  29.3 136.9 233.                             
> > hunter    Linux 2.4.27-  19.8  74.0 146.                             
> > hunter    Linux 2.4.27-  19.7  74.4 134.                             
> > hunter    Linux 2.4.27-  19.5  77.8 137.                             
> 
> Degradation #2: pipe and AF_UNIX latencies. This can likely be profiled
> without NMI's.

Is there an easy way to run only this one? I can profile that.
Larry? 

--
vda

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