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Re: Sleazy FPU optimization
On Mon, Feb 11, 2008 at 07:43:09PM +0100, Joerg Sonnenberger wrote:
> On Mon, Feb 11, 2008 at 05:27:16PM +0000, Matthias Scheler wrote:
> > Linux 2.6.20 and above has an interesting optimization for lazy FPU
> > context saving:
> We've been discussing whether or not it is worth to do lazy FPU context
> saving at all. Most programs will use the FPU on i386 anyway, e.g. if
> printf is used. I'm not sure it will actually help.
1) Why would using printf for integers need the fpu
2) a fair number of context switches don't end up in userspace (or
only return there for a veru short time) doing a full FP save/restore
on these is likely to be expensive.
3) I suspect that some programs (like make) hardly ever use the FPU at all,
but will do a lot of context switches.
David Laight: david%l8s.co.uk@localhost
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