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Re: [Qemu-devel] Benchmarking linux-user performance
From: |
Emilio G. Cota |
Subject: |
Re: [Qemu-devel] Benchmarking linux-user performance |
Date: |
Fri, 10 Mar 2017 21:25:06 -0500 |
User-agent: |
Mutt/1.5.24 (2015-08-30) |
On Fri, Mar 10, 2017 at 12:48:31 +0100, Peter Maydell wrote:
> On 10 March 2017 at 12:45, Dr. David Alan Gilbert <address@hidden> wrote:
> > * Emilio G. Cota (address@hidden) wrote:
> >> x86_64 NBench Floating Point Performance
> >> Host: Intel(R) Xeon(R) CPU E5-2690 0 @ 2.90GHz
> >>
> >> 1.88
> >> +-+-+---+--+---+---+---+--+---+---+---+---+--+---+---+---+--+---+-+-+
> >> | + + + *A*#*A* + + + + + + + + + + + +
> >> |
> >> 1.86 +-+ *** ***
> >> +-+
> >> | # # *A*#***
> >> |
> >> | *A*# # # ## *A*
> >> |
> >> 1.84 +-+ # *A* *A* #
> >> +-+
> >> | # # *A*
> >> |
> >> 1.82 +-+ # # ##
> >> +-+
> >> | # *A*# #
> >> |
> >> 1.8 +-+ # # #*A* *A*
> >> +-+
> >> | # *A* # #
> >> |
> >> 1.78 +-+*A* # *A* #
> >> +-+
> >> | # ***# # #
> >> |
> >> | *A*#*A* # #
> >> |
> >> 1.76 +-+ *** # #
> >> +-+
> >> | + + + + + + + + + + + + + + *A* + +
> >> |
> >> 1.74
> >> +-+-+---+--+---+---+---+--+---+---+---+---+--+---+---+---+--+---+-+-+
> >> v1.v1.v1.2v1.3v1.4v1.v1.6v1.7v2.0v2.1v2.v2.3v2.4v2.5v2.v2.7v2.8.0
> >> QEMU version
> >
> > I'm assuming the dips are where QEMU fixed something and cared about corner
> > cases/accuracy?
>
> Given the scale on the LHS is from 1.74 to 1.88 my guess is that the
> variation is in large part noise and the major thing is "our fp
> performance is bounded by softfloat, which doesn't change and is
> always very slow".
It isn't "measurement noise" -- if you look at the PNGs the measurements
are very stable (all points have error bars): http://imgur.com/a/nF7Ls
It's true that performance here varies very little. This is just the
result of Amdahl's law, as you point out. (upon re-reading your message,
I see that perhaps what you meant by "noise" is exactly this.)
E.