Subject: Re: Slow X applications [was Re: X server as a Unix system process]
To: Chris Dearman <>
From: Jukka Marin <>
List: tech-kern
Date: 07/28/1997 15:26:16
[X slowness]

> FWIW, we've seen the same behaviour with a completely different setup
> (a CAD application running on a Sparc system using SunOS 4.1.x).
> After a while, the application starts to send single requests instead
> of batching them up.  This phenomenon only became apparent when we
> started using the application over an ISDN link, where the bridging
> delays made the behaviour obvious.

Hm.  And I was hoping my problem was caused by some odd linux libraries
or something like that.  Well, I guess it isn't, then.

> Later, Jukka reported that running his application with an X server
> that does not use mmap/munmap, made things go much faster.  I suspect
> that the application is still doing small writes, but the round-trip
> time between the application and the X-server is now low enough
> that the small packet size is masked.

Yes, I believe this is the case.  I still haven't tried building a
profiled version of the X server to see why it runs so slow with
mmap/mumnap enabled, but I've been satisfied with the X performance
with the old memory allocation scheme.

> I realise that this is probably an X related issue now, but if anyone
> else has seen this behaviour or has an idea on what may be causing the
> sudden switch to small packet sizes, I'd appreciate your views.

I have talked to some X developers about this, but they say it's the
client which makes the decision to use small packets, not the server.

I'd be interested to know what really is behind of this problem.



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