Re: [uml-devel] Recent patches of note

[Bodo Stroesser <bstroesser@fujitsu-siemens.com>]

Jeff Dike wrote:
> I'd like to call attention to some recent patches that may be of interest
> to people before they hit mainline.  These are all on my incremental patches
> page, http://user-mode-linux.sf.net/patches.html
> 
> First, sched-starve (http://user-mode-linux.sourceforge.net/work/current/2.6/2.6.12-rc6-mm1/patches/sched-starve)
> 
> This fixes a timer initialization botch which resulted in soft lockup
> warnings in recent kernels, total non-responsiveness (i.e. nothing
> else would be scheduled) under any workload which avoided idling the
> kernel, and may be responsible for the load average >= 1 problem.
> 
> I don't see that last here for some reason, so I'd like some
> confirmation (or not) that this patch fixes that.
> 
> Second, I implemented soft interrupts, which reimplements interrupt
> enabling and disabling with a flag rather than with sigprocmask.  This
> cuts down hugely on the number of system calls that UML makes,
> resulting in a very noticable performance increase.  This patch, plus
> the other system call reducing patches which immediately follow it,
> speed up my kernel builds by 20-25%.  By far the largest piece of this
> is softints, although skas-no-flush-kernel also is noticable.
Great!

> 
> I'd like people to check out softints, at least, and report any
> problems.  It's running fine here, but interrupt handling is a
> sensitive area, so I'd like to know people are running it without
> problems before pushing it to mainline.
> 
> 				Jeff
Currently my time is *very* limited, so I can't test. Reading the patches
only the one that makes me worry is "dont-save-fpregs".
To not save fpregs on every syscall or interrupt is O.K.
But you also have to modify signal-handling, that currently relies on
fpregs being saved. And you have to save and restore fpregs in switch_to
for SKAS3 and also for SKAS0, if processes share the same mm.
Then, I think special handling is needed for the fpregs in copy_thread
and probably in execve also.

	Bodo


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