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Re: 2.4 kernel performance?

Part of the problem is the linux default timer rate of 100hz.  This just
isn't suitable for fast polling.  Unmodified I get turnaround rates for a 3
byte ping followed by a 3 byte pong to be around 150ms.  My solution has
been to kick up the timer tick rate to as high as 3200hz.  This drops the
ping/pong time to 4ms.

     set max flush time to 1

     set HZ to 3200

     at the bottom where the divisor from 19200hz is 192, change the
divisor to 6

I dunno what this last module is;  it wasn't in e-linux, but complains
about the higher clock rate.
     between define SHIFT_HZ=10 and the endif, add:
     #elif HZ >= 1536 && HZ < 3072
     # define SHIFT_HZ   11
     #elif HZ >= 3072 && HZ < 6144
     # define SHIFT_HZ   12

go back to devboard_lx
make kernel; make files;  make images

Adam Felson
HID Corporation - Engineering
11674 N. Huron Street
Denver, CO 80234-2924
(303) 453-3362

                    Adolfsson"              To:     <matthew.hook@xxxxxxx.nz>,                  
                    <johan.adolfsson        <dev-etrax@xxxxxxx.com>                               
                    @xxxxxxx.com>              cc:                                                
                    Sent by:                Subject:     Re: 2.4 kernel performance?           
                    05/08/01 01:29                                                             

The serial drivers are differently, some features of the elinux driver
has not been ported to 2.4 yet.
One thing that is different is the DMA timeout handling,
in 2.4 it's 8 jiffies (MAX_FLUSH_TIME) and not configurable as
it is in elinux (it probably should be configurable).
If you have short messages used for handshaking this could have
a big impact.
You can try decreasing MAX_FLUSH_TIME in arch/cris/drivers/serial.c
and see if that helps.


----- Original Message -----
From: <matthew.hook@xxxxxxx.nz>
To: <dev-etrax@xxxxxxx.com>
Sent: Tuesday, May 08, 2001 06:24
Subject: 2.4 kernel performance?

> Has anyone noticed whether the 2.4 kernel on the Etrax 100LX has
> significantly slower
> performance than uClinux?
> I've spent the best part of an afternoon observing that code compiled
> running on uClinux
> runs about 4 times faster than code on the 2.4.... however, it might be
> e.g. the com port
> drivers under 2.4... my software basically reads data from one com port
> writes it to another
> and vice versa, but the throughput has dropped by more than 1/4 on Linux
> 2.4.
> Has anyone noticed anything similar?