Re: Short question regarding generic_make_request()

From: Steffen Persvold (sp@scali.com)
Date: Mon Feb 04 2002 - 06:56:45 EST

Ingo Molnar wrote:
>
> On Mon, 4 Feb 2002, Steffen Persvold wrote:
>
> > [root@damd1 root]# ping sci4
> > PING sci4 (192.168.4.4) from 192.168.4.3 : 56(84) bytes of data.
> > 64 bytes from sci4 (192.168.4.4): icmp_seq=0 ttl=255 time=238 usec
>
> > For simplicity I'll say ~200usec. When I change the receive handler
> > from a tasklet to a kernel thread, the numbers look like this :
> >
> > [root@damd1 root]# ping sci4
> > PING sci4 (192.168.4.4) from 192.168.4.3 : 56(84) bytes of data.
> > 64 bytes from sci4 (192.168.4.4): icmp_seq=0 ttl=255 time=4.215 msec
> > 64 bytes from sci4 (192.168.4.4): icmp_seq=1 ttl=255 time=5.728 msec
>
> this shows some sort of wakeup or softirq handling irregularity. A number
> of softirq latency bugs were fixed, i'd suggest to try this with any
> recent kernel (or recent errata kernel rpms).
>

You are right indeed. I tried a vanilla 2.4.17 kernel at it performs well with a kernel thread (even
better than a tasklet actually) :

TCP STREAM TEST to sci9
Recv Send Send
Socket Socket Message Elapsed
Size Size Size Time Throughput
bytes bytes bytes secs. MBytes/sec

262144 262144 262144 10.00 157.73

Any idea when this bug was fixed (haven't tried the latest RedHat errata kernel yet, but will do).

I guess now that I can use the kernel thread without loosing performance I can start using
generic_make_request() in the block device server.

Thanks for all the help,

Regards, 

-- 
  Steffen Persvold   | Scalable Linux Systems |   Try out the world's best
 mailto:sp@scali.com |  http://www.scali.com  | performing MPI implementation:
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This archive was generated by hypermail 2b29 : Thu Feb 07 2002 - 21:00:33 EST