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SubjectRe: Short question regarding generic_make_request()
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:
Tel: (+47) 2262 8950 | Olaf Helsets vei 6 | - ScaMPI 1.13.8 -
Fax: (+47) 2262 8951 | N0621 Oslo, NORWAY | >320MBytes/s and <4uS latency
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