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Date: Tue, 18 Sep 2001 13:02:27 -0700
From: Andrew Morton <akpm@zip.com.au>
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To: Andrea Arcangeli <andrea@suse.de>
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Subject: Re: 2.4.10-pre11: alsaplayer skiping during kernel build (-pre10 did 
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Andrea Arcangeli wrote:
> 
> I now have an update ready for Linus to merge that should fix the few
> leftovers I had in the very first release of the vm rewrite but of
> course I will be interested to hear about any regression/progression
> about those changes, I'll post them in a few minutes in CC to l-k.
> 

Please include Andi's likely()/unlikely() change - it's nice.

I can't measure any obviously new causes of latency in your
VM.  It's nice that you've paid attention to this in various
places.

The main culprits now are the file IO and dirty buffer writeout paths:
up to fifty milliseconds in each.

I suggest you stick scheduling points in generic_file_read(),
generic_file_write() and write_locked_buffers() and then dispose
of the copy-user-latency patch from -aa kernels.

With the above fixed, the main source of latency is
/proc/meminfo->si_swapinfo(). It's about five milliseconds per gig
of swap, which isn't too bad.  But it's directly invokable by
userspace (ie: /usr/bin/top) and really should be made less dumb.